jimkleban
I too have a similar problem with SONAR only.  My noise is directly related to activity on my PC... it is not being recorded but is always there but only over the powered speakers and not the headphones.  When SONAR is not running, the noise goes away.  Other audio programs do not create this noise (that is, MEDIA CENTER, SOUNDFORGE or plugins that can run outside of SONAR).  The density of the noise changes when I change the views within SONAR. 
 
I too would describe the sound as CHATTER and not a constant noise... the chatter sounds like it is related to PC activity and not just random over the air noise.
 
I have added a power condition to my system to no avail.  I have changed all my speaker cables to BALANCED TRS. I have changed powered monitors from M AUDIO to JBLs.
 
This noise only shows up when SONAR is in FOCUS on my system.  If SONAR is running and I minimize the application, the noise goes away.
 
I have given up on fixing this since it doesn't affect the audio at all, just the monitoring and share my experience

You aren't by chance running a Nividia graphics card ? I smell a connection....

   To touch on some of the things mentioned above. It does it on all projects, and it does it all the time whether SONAR is open or not. It only happens when his computer is plugged into his interface. We've tried different interfaces and that is not the problem.
   His machine is a desk top tower...mine is the laptop.  It was built by a friend who has built his own computers for his home DAW's which have always worked fine, but he's not a dealer. However, he would be the one to do any serious checking inside the cover.
   I don't know if any ports are USB 3, but it makes the noise with all of the USB ports.
   I don't know about the graphics card.
   When we did the experiment last night everything was the same....monitor, speakers, Interface, location, etc. To do the experiment we had a USB coming from his computer and a separate USB cable coming from my laptop. We'd plug his computer into the Focusrite interface and get the noise. When we unplugged it the noise stops. Then we'd plug my laptop into the same interface and there is no noise. Then, plug his back to the interface and the noise starts again immediately. We were using two separate USB cables, but he's tried other cables the past few days and that doesn't seem to matter. No matter what USB cable, the noise starts as soon as his computer is hooked to the interface.
   That's a good point about whether it just started or has it always done it. I'm pretty sure it was fine in the beginning and this noise started later. That would indicate that maybe it is a connection that's come loose. My friend with the computer noise will probably be in later today to answer some of the details that I don't know the answer to. After the experiments last night we're practically sure that the trouble is with his computer, but we don't know where.
    Thanks again for all the input. Looks like several others here have had the same, or similar, trouble, so I hope this thread helps others correct the trouble.
DS

If you're powering the interfaces with USB, do you have an AC power supply for either interface?

That is a good point about powering the audio interface

I get a constant "whining" noise if I run my audio interface (Maudio Fast Track Ultra) on USB power, which disappears when I run it with its own power supply plugged in

One other thing, (I'm not sure if this was already said), is to make sure the onboard audio is turned off, which if it was set up as DAW, should be.

MacFurse
One other thing, (I'm not sure if this was already said), is to make sure the onboard audio is turned off, which if it was set up as DAW, should be.

True, but I have had Win 10 updates turn it back on.  Now I check after each update.

MacFurse
One other thing, (I'm not sure if this was already said), is to make sure the onboard audio is turned off, which if it was set up as DAW, should be.

I use onboard audio for everything except SONAR, with my 16x08 used exclusively for SONAR.  My speakers aren't chattering.
 
If the DAW in question is sharing the same USB hub, whether internal or external, with external drives or other high demand gear ...

If the sound is really static-like i. e. it sounds like a scratchy coarse crackling in the situation you describe, then there is almost certainly an intermittent loose connection or near connection with electrical arcing across the defect. It is most probably a bad solder joint on the motherboard. If it were just a bad joint at a single USB socket, then it would not affect all sockets, so more probably it represents a defect at a common ground point.  A loose or dirty plug could also be the problem. The only user serviceable option at this point would be to remove and clean the plug connectors to the front panel USB sockets and the power supply, but that is a real longshot. Testing would be a **** involving tracing the circuits on the board to check for unexpected resistance or noise/crackling with a signal tracer.  
 
I probably missed it, but you have checked for external power issues by plugging his computer in at your house and running the tests there?

In post #1 you said the USB cables were eliminated, but in post #6 you said two different USB cables, so not eliminated. Just checking ...

We were not using a powered Focustite, but this is something he can try, and that's a good idea.
We did not take his computer to my house. But my laptop worked fine in the electrical outlets at his house.
Yes, we used two separate USB cables in the test last night, but he has tried other USB cables previously with no improvement. That's what I meant about eliminating his USB cable as the problem. There was noise on any USB port and with any USB cable he used.
And good idea about just giving the inside a visual to see if anything looks loose.
And another good idea about the on board audio. I assume it is turned off, but now that you mention it we need to check that also.
So, this has been very productive. Now we have more things to check, and with a little good fortune, hopefully if will be an easy fix from some of the suggestions here. I'll keep you updated.
You guys have really gone above and beyond to help with this, with more options than I could imagine. We really appreciate all the time and info you're putting into this. We'll keep checking and hopefully get it corrected without having to buy anything or do any soldering project.
DS