The ground lift is not something I really suggest or do, but I mentioned it.  Usually, as long as the device its attached to is properly grounded the attached device will be too.
 
Obviously the best option is to only buy devices that properly ground, but who knows.
 
My biggest audio challenge was shielding (RF Shielding) a studio in Kansas City, Mo (Big K Records) that was 1 block from an AM radio station transmitter site.  I could never get 100% out but got it out of the board and recording equipment (all analog tape at the time).  I couldn't get it 100% out of the headphone distribution system but it was low enough it didn't interfere with sound levels.
 
BTW, ex W5DVO, K3FFZ, ZD8JES
  

fireberd
Usually, as long as the device its attached to is properly grounded the attached device will be too.

 
Still not good advice. Lifting the earth connection on any equipment is just downright dangerous. You cannot rely on the audio earth connection between an earthed and non earthed equipment either to provide a solid ground. It might be quiet but in the event of the live mains wire coming into contact with the metal chassis of one of the items concerned then the audio earth may not be enough to save you.
 
A much better and safer way is to leave all items grounded, and if a ground loop appears then solve it by lifting the earth connections in some of the audio connections, not the power.
 
Using balanced audio connections wherever possible is a great start. (especially between your active monitors and what is feeding them e.g. interface monitor outs.) A lot of stuff has balanced connections these days and many don't know it and are using unbalanced leads to connect stuff.  Not only do you get great noise rejection with balanced connections but a 6 dB volume boost too for free.  Many synths have balanced outputs and many line inputs on mixers are also balanced as well. Use em!
 
Sometimes when you connect things like iPads or laptop outputs you can pick up hum, noise or other sounds. There are also ways to connect non balanced outputs into balanced inputs. e.g. by wiring into the balanced input using the balanced connections only and not the balanced inputs earth. This can also solve many hum and noise problems too.
 
Plugging your entire studio into a single power circuit is also a good thing to do. It puts all the earths in the system at the same potential and will minimise ground loops. Your entire studio will not draw enough power to trip the breaker either.
 

Ha!  It worked.  I didn't want to just come out and ask for detailed advice for my particular situation (as well as being helpful for others, I'm sure).
 
I like the idea of hiring someone local, though I'm hoping an excellent electrician will be able to do what's necessary (in fact, I'll determine if he/she is excellent by their reaction to my instructions/questions).
 
I learned the test-as-you-go lesson the hard way.  Several times.  What's the definition of insanity again...
 
Great stuff, thank you.  I'm excited to be able to at least try to address this from the, ahem, ground up.

I won't get into a pi..ing match with you but if there is a ground connection (maintained) between the two devices it is grounded.  It is not the best option but has worked for ages for musicians.

I am referring to high voltage mains situations of course here.  I witnessed a situation where the active mains wire came into contact with the chassis of the unearthed device that was supposed to be earthed via the audio connection (to another grounded device) The mains earth was removed from one of the devices to prevent a ground loop via a double adapter with its ground pin removed.  The audio connection between them was completely destroyed in a microsecond and the chassis of the unearthed device became lethal and nearly killed someone who touched it. (240 volts remember here!) 
 
So no, to rely on the audio connection to ground a device safely is a myth.  Some earth ground audio connections might only be relying on a minute amount of contact to ground via the plug/socket where a properly grounded chassis with a wire terminated to a tag bolted to the chassis is much better.  Some switchboard circuit breakers will trip though in a microsecond and save you but you cannot always rely on that either. 
 
Do no unearth your mains devices. It is simply dangerous. 
 
It is possible to leave both devices grounded and lift the earth connection of the audio cable at one end between them instead. (As long as one end is still grounded, the shield of the cable will still do its job) Same result but much safer. Harder to do though, requires making a special lead. Lifting mains earths is much easier. 
 
Of course if the power supply is low voltage DC for both devices then yes, less danger. Or the devices are double insulated. Different for 240 volts though. Although I have have heard of situations where the mains input to a DC power supply also found its way into a low voltage DC device too and that was not pretty either. 

Afraid I can't agree completely, but your first point is spot on.

Jeff Evans

fireberd
Usually, as long as the device its attached to is properly grounded the attached device will be too.

Still not good advice. Lifting the earth connection on any equipment is just downright dangerous. You cannot rely on the audio earth connection between an earthed and non earthed equipment either to provide a solid ground.

 
Here's the thing, and neither Jeff nor I seem to be saying it well. It is NEVER good advice to suggest bypassing a safety ground. If two pieces of gear are connected, via shield, when only one is connected to earth ground then it is true that both are grounded. But you are now depending on that shield to carry a lethal current to ground, and more than likely it will fail and you will carry that current to ground.
 
It seems that everyone who understands grounding and shielding assumes everyone else does too. That's why I will often jump in when posts suggest defeating safety ground. To someone that is more musician than electrical engineer that might sound great. But they don't understand the safety implications.

That's why I get so insistent on the subject. I'm not trying to start - or sustain - a pi$$ing contest!
 
Part of the confusion stems from our mis-use of the terms ground and common. Ground is considered this mystical point where no amount of current flowing in or out can change the potential - but wait, that definition is missing a word - "difference". A potential difference can not exist at a single point, so we need to know with respect to what (or where.)

All of which is digging deeper than necessary. Always connect safety grounds and you don't have to think about it.
 

Jeff EvansA much better and safer way is to leave all items grounded, and if a ground loop appears then solve it by lifting the earth connections in some of the audio connections, not the power.

 
Also true, although I'd go one step further, consider "Aggressor" and "Victim" and treat accordingly.
 
Embarrassing tale I've told too many times to care any more - back in the bad old days I had this lovely Tangent console that I was rebuilding. For grins I decided to try the "huge copper bar" approach that I knew some of my heroes were using to quiet their consoles. It was expensive, tedious, time consuming, and dang, it worked. It worked really well!
 
Turns out we were all fixing the right problem with the wrong solution! As part of the huge copper bar solution we were terminating the shields outside the chassis. Yes, I felt kind of dumb. And yes, I was able to re-sell that copper bar, for a tad more than I paid for it, but I'll never get the hours spent drilling and threading!
 

Jeff EvansUsing balanced audio connections wherever possible is a great start.

 
And herein lies maybe the biggest source of confusion. Every source can be treated as balanced. And all you need to connect a balanced source to a balanced input is two wires, although it helps tremendously if they are twisted.
 
That leaves the input as the potential (excuse the pun) problem. If it is a single ended input you will need to do something to make it differential - you can add a transformer (ideal, but expensive) or you can add an active device. That's it! Meaning there really is no reason not to use balanced interconnections everywhere.
 

Jeff EvansNot only do you get great noise rejection with balanced connections but a 6 dB volume boost too for free. 

 
Part 2 of the great audio myth - a balanced connection is not dependent on signal symmetry, nor does it require that both input pins be driven at all. The ONLY requirement for a balanced connection is that both input pins see a equal impedance to ground. That's the definition of a balanced input. And that means that  the only requirement for the source is that it presents an equal impedance to ground on both legs.
 

Jeff EvansThere are also ways to connect non balanced outputs into balanced inputs. e.g. by wiring into the balanced input using the balanced connections only and not the balanced inputs earth. This can also solve many hum and noise problems too.

 
I think you are saying that correctly, but without a picture it could be confusing. I usually suggest folks read several Rane Notes to see the pretty pictures. Here are my go-to references:
Sound System Interconnections
Grounding and Shielding
Why Not Wye
Pin 1 Revisited
(these next two get a little deep, but are still worth skimming)
Shield Current Induced Noise
Considerations in Grounding and Shielding Computer-Controlled Audio Devices
 

Jeff EvansPlugging your entire studio into a single power circuit is also a good thing to do. It puts all the earths in the system at the same potential and will minimise ground loops. Your entire studio will not draw enough power to trip the breaker either.

This is great for really small systems, but it can cause as many problems as it causes, especially since most folks will stop there, assuming this is the cure-all.

All of this goes back to my previous assertion about safety - those of us with experience and education need to do a better job separating fact from fiction. We need to stop assuming everyone understands this stuff as well as we do. That's no different than assuming everyone has studied harmony, counterpoint, and orchestration when discussing sample libraries!
 
So we need to choose our words carefully, and sometimes we need to type a lot.
 
And now our regularly scheduled aside:
 

fireberdMy biggest audio challenge was shielding (RF Shielding) a studio in Kansas City, Mo (Big K Records) that was 1 block from an AM radio station transmitter site.

Wow does that bring back bad memories - in a good way! My biggest challenge was a combo (AM/FM) co-located with the AM transmitter. I was still a wee lad (might have still been in college) and in completely over my head! I had two things going for me:
1) the previous engineer was a genius, and the AM control room was quiet, so I studied what he did, and adopted a telescoped shields solution that copied his approach. And it worked!
2) while a radio station needs to be quiet, it doesn't need to be recording studio quiet, so my goals were somewhat less demanding. You had your hands full!

fireberdBTW, ex W5DVO, K3FFZ, ZD8JES

Why "ex"

Thanks Bill. Nicely put for us lay people. Well at least me.

I agree the ground lift is not a permanent solution, but is useful in troubleshooting.  Just as isolating from the rack rails is not a real permanent solution but also good during troubleshooting.  
 
Bill, the "ex" is because of my laziness and mistake.  I moved and thought I had a year to get the licenses (I also had a 2nd class FCC Radiotelephone) renewed when in actuality when I got around to it, it was over the 1 year grace period.  I would have had to retake the tests and I didn't have any ham equipment and was not working where the FCC license was needed.

fireberd
I agree the ground lift is not a permanent solution, but is useful in troubleshooting.  Just as isolating from the rack rails is not a real permanent solution but also good during troubleshooting.  

 
I'll go so far as to agree that if you have a strong background both of these can be used as troubleshooting tricks. Isolating from racks can even be a more permanent solution. Several of my racks (which are gorgeous, custom made by a cabinet maker buddy) are all wood - it's a pain to drill the rails, and if I ever revise the studio I'll likely get rid of the wood rails and just stick Middle Atlantic Rack Rails in there!
 
Anyway, the point I want to make (maybe Jeff too, can't speak for him) is that if someone knowledgeable talks about defeating safety ground someone with less knowledge may stop reading right there. It is safer to just not talk about it. My two cents.
 

fireberdBill, the "ex" is because of my laziness and mistake.  I moved and thought I had a year to get the licenses (I also had a 2nd class FCC Radiotelephone) renewed when in actuality when I got around to it, it was over the 1 year grace period.  I would have had to retake the tests and I didn't have any ham equipment and was not working where the FCC license was needed.

Thought that might be the case. I'm in the same boat on the 2nd radiotelephone - I wasn't paying attention, wasn't working in broadcast at the time, and it lapsed, and I'm too lazy or too dumb to survive the test a second time. The ham license keeps me amused, and I still don't work in broadcasting!

I used the 2nd Class Radiotelphone when I worked for a Motorola 2-way radio dealer (like in police, fire vehicles, etc).  The 2nd class was required. Capital Radio Communications in Lemoyne, Pa (Harrisburg suburb).