Buzzing monitor, some advice needed from electricity boffins

As I posted here some weeks ago, there was a power surge in my building and it knocked out my Equator Audio D5's which unfortunately I'd left on when I went out that day. Dead as dodo's. So I sent them back to EA and they told me that they needed new amps and offered to do the repair for around $140. With shipping the whole affair sprang to around $180. Given that they only cost me $300 (got 'em on sale), it's was a bummer to have to lay out more money, although it certainly wasn't EA's fault that they blew. 
 
Anyway I got them back a while ago and all is not good. One of them buzzes like crazy (almost like a guitar amp, not the usual faint hiss that you expect) and it seems to be picking up interference from my DAW - you can hear things like moving the mouse pointer around, moving windows around etc. Also, the buzzing one is noticeably quieter than the other one at the exact same sensitivity level (there's a sensitivity knob around back). Not good. 
 
While waiting for them to come back, I had bought a Furman power conditioner to protect against further spikes and interference. So they're both plugged into that, as are my DAW and some other stuff. 
 
The buzzing only happens when the monitor is connected to my interface. It happens whether I connect it to the right or the left output. And here's what I think is a very important fact - the other monitor does NOT buzz. If I swap them out and hook up the other one with the exact same cables to the exact same output and put it on the exact same spot on the desk, it doesn't buzz. Quiet as a mouse. 
 
I let EA know this but they responded back and said they were sure it was a ground loop issue and pasted some advice regarding DI-boxes and ground lifts into the email. So they've basically given me a pretty long winded set of things to try. But before I get into all that, I just cannot get past the fact that this is only happening with ONE of the monitors, and the buzzing one is quieter than the other one. I did relate this information in an earlier email and I don't know whether they just ignored it or whether they're still convinced it's a ground loop issue despite this. Neither monitor buzzed like this before they blew, and their gain was matched perfectly. Now, signals that should be dead center are skewed off toward the non-buzzing one unless I adjust the sensitivity of the buzzing one to match. Of course I don't wish to do this because I'd much rather not have the balance of them entrusted purely to my judgment. They should be the same volume, period. 
 
Any thoughts? I know they're probably thinking "goddamn it, not this guy again...." so I'm not sure if I should get all gung ho about it at this stage, especially since I'm pretty clueless when it comes to electrics. 

Perhaps. Although that still doesn't explain in my mind why only one of the monitors is affected. 

Plug just the 'good' monitor in at the location the buzzing one occupies.
 
Does it buzz?
 
Y: you have some issue external to the monitors.
N: Send the buzzing monitor back to EA to fix properly.

Well it's only the one which buzzes. And it only buzzes when connected to my interface. But if connect the other one with the exact same cables and sit it at the exact same location, it doesn't buzz. I did explain this to EA in an email, but they're going with the "ground loop" theory anyway. I'm just wondering if they've actually processed the info I gave them and are still going with ground loop (ie not their responsibility) or whether they've missed that info. I'd like to be in a position of at least some knowledge before I pursue it.

Thanks John, that's what I thought. However, I am puzzled by something else, which is that the monitor doesn't buzz unless my DAW is turned on. If I boot my DAW, I hear that bleep-bleep interference which sounds a little like a dialup modem while the computer starts up. Then it settles into a steady buzzing which changes with activity in the computer (i.e. programs loading, mouse activity etc). So it's definitely picking something up from the computer. What I'm wondering is, when you say "bad amp" could that include some kind of lack of shielding?
 
Another interesting piece of info I just discovered: Everything is powered by a dual socket. I have two strips connected to these outlets. One is the Furman unit, to which I have attached the DAW, the monitors, my external HD adapter, my printer, one of my displays a laptop and a phone charger.  The other is a cheapo anti-surge strip to which I have plugged in my other display, a router, modem and a desk light. If I unplug this cheapo strip from the wall, I hear an additional low frequency buzz in the monitor as well as the usual buzzing. Just another piece of the puzzle I guess.

Yep both have the same sensitivity setting. There are also settings for free standing, wall or corner and they are both set to wall.

This is almost certainly a flubbed repair job. Hopefully the technician will be able to reproduce the problem and figure out his mistake. Chances are they did not replace the amplifiers with original equipment, but instead used generic replacements. There could be issues with product quality in the cheap amplifiers they stuck in there, which they probably chose at random from Parts Express.

It could definitely have an impact on sound, as well as that problem with volume imbalance that you were talking about before.

Is it feasible to open 'em up to see if the circuitry inside looks identical in both?