(I am very new to all of this, so please keep that in mind).
 
I have a Roland FA-08 plugged into a Tascam US 4x4 via TRS cables.  Tascam is USB into a homebuilt computer.  I also have the FA08 plugged in USB into the computer.  I have two JBL monitors plugged into the Tascam for output.  I just purchased a used studio desk with a tray for an 88 key board and put everything together this past weekend.
 
I am not really familiar with the Tascam, but I have it up and working well.  I am just learning about recording audio and Midi (as I said, I'm really new).  I noticed after I got everything together this weekend I have quite a bit of electrical noise in JBL monitors when I turned up the line out on the Tascam.  The noise is substantial.  I tracked down the noise to the USB cable that goes from the FA08 to the computer.  From the keyboard tray, I had the power, TRS cables, and USB all nicely zip tied together and mounted to the desk so I could pull the keyboard tray in and out easily.  Obviously, zip tieing the USB together with the TRS cables is causing the noise (as soon as I disconnect the USB from the FA08, the noise goes away). 
 
To the point, I think I have a few options..
 
1)  Is there such thing as a better or "shielded" 1/4 cable I could use that would withstand the USB noise?  What I have now is 6'  unbalanced cables from Guitar Center.  If I could buy something better, I would prefer that, because my option number 2 is:
 
2)  Drill some holes and modify the desk to physically separate the TRS from the USB.  Even so, I think at some point they will be in contact, but it would only be for a few inches.  If they are close to one another for a few inches I don't know if that will actually solve the problem.  
 
3)  Just simply disconnect the TRS cables, and record only through the USB, and use the Tascam only for the output to the JBL.  I would prefer to keep the Tascam for the output, as that is less cables going to the keyboard.  In addition, I am saving for a Moog which would require the Tascam.
 
As I said am trying to learn.  The noise is too much, and I know I need to do something about it.
 
Thank you.

There is a bit of a contradiction in your description. You talk about TRS cables (which would be balanced) and then mention unbalanced cables (which would be TS connectors).
 
TRS/XLR (i.e. balanced) cables are shielded by design - interference along the signal path cancels out when the signal is recombined on the other end. So if your cables are unbalanced and you can use balanced ones, you should get balanced ones before trying anything else ... but check interface specs and monitor specs to see if these really accept balanced connections (TRS/XLR) because if one end is unbalanced connection, then changing cables won't help.
 
However, this could also be a case of "dirty" USB power supply or some manifestation of a ground loop. Try a different USB port or try with another PC (best a laptop run on battery) and see if the USB noise persists

Sorry for the confusion.  These are unbalanced cables.  I thought everything was TRS.
 
All the USB ports in the computer exhibit the same noise.  I can't really change computers, because this is my DAW computer.
 
 

If your DAW computer is a laptop then unplug its power and run it off of batteries for a test. Does the noise go away? 

DAW is a homebuilt PC, not a laptop (see signature for details)

After some further research and testing, I think it is a USB ground look. 

So, for me, I wonder if it is just as easy to simply remove the USB connection. I don't "technically" need it at all. I was just playing around with different input/outputs in the DAW.

So, I now have two options:
1) Disconnect the instrument cables and record only via USB, and use the AI as output only, or
2) Disconnect the USB and use the AI for everything. I could do midi for VSTi through a Midi cable through from the FA to the Tascam.

Is there a benefit one way or the other?

Make sure your interface and powered speakers are plugged into the same outlet, so they share a common ground.
 
Your interface does not appear to have balanced outputs, so balanced cables aren't going to help and will only drop signal level to the monitors.
 
Do you hear the noise in headphones plugged into the interface's headphone jack? It's possible the USB cable is radiating noise, in which case you might look into a higher-quality shielded USB cable. 
 

I'll check the headphones tonight.  So plugging in the AI and the JBLs into the same strip, and the keyboard and computer into the other would prevent a loop?  I thought that is they way I had it set up, but I will have to check.

I looked and the outputs of the 4x4 are balanced.  However, I was referring to the TS cables I have between the keyboard and the interface, not the interface and JBLs.  I guess this would matter as well....
 
Still thinking though the best solution would be to just get rid of the USB, as it seems pretty superfluous.  Just not sure.
 
 

Almost always a grounding issue.
Power the entire setup from a single outlet.
That'll help eliminate ground issues.
 
Sometimes a poor quality USB cable can also induce noise.
Try swapping the cable for a higher quality cable.
 
USB connection (in-and-of-itself) isn't the problem