When you used your laptop, did you have it plugged in or was it running on batteries?

Plugged in. And he's tried every receptacle in the room and also power strips and everything imaginable and nothing changes.

Some time ago I had an Asus / AMD that would do a lot of strange things if I used the supplied "overdrive (overclocking)" options supplied by the manufacture. I only remember that I could not run with the overdrive enabled. Don't know.

1. Does this happen with all projects?
2. Is his computer shop bought or self-built?
3. Is this something new or was it fine at one point?
4. Are you sure he's not plugging into USB3 ports? If so, change to USB2

I would open up his machine and try and get an idea of the PSU - what's it capable of driving and does this exceed by a wide margin the current demands of everything inside? (Yep, this means listing everything drawing power and searching on t'interweb for it's power requirements

I use a Roland GR-55. If I have the audio outputs and the USB hooked up at the same time, I get a high frequency noise from the USB. Unplugging either the audio (and allowing the GR-55 to be the audio interface), or disconnecting the USB cable eliminates the noise. Is it possible you have a similar situation in one of the pieces of USB gear being used?

A lot has been suggested already. my first guess would have been a grounding issue as laptops seem susceptible to those than desktops.
 
Have you ever tried to disable the graphic card and run with the onboard graphics?? Graphic cards can cause all sort of weird issues.

JustGotPaid
 
We can probably check for loose wires, but neither one of us is knowledgeable enough to start working with or testing the motherboard. If he has to try that I think he should take it back to the guy who built it. This is a special build DAW. This is not a desktop tower from Best Buy or New Egg or some other computer place with a tower ready to go out of the box. It was all put together locally and very well could have a loose wire or a deficiency in shielding or grounding.
 
DS

If opening up the case voids the warranty then by all means take it back. Personally after all of the testing that you did and the fact that it strongly points to the computer I would take it back.  If he is a reputable dealer he will work with you in solving the problem.

I had something similar to what you describe, and it was because I put my monitor (screen) on top of my interface, a scarlett 20i18. Moved it away, and all was good. Now I keep the interface as far from everything as I can. But, with yours being OK on headphones, but not on the monitors, that's more likely still to be an earth loop somehow, or crook lead. Just confirming, PC/screens, interface and monitors, are all plugged into the same outlet? You have tried a different usb lead, and tried different cables to the monitors? You have removed all other USB devices connected to the PC except the wireless KB/mouse, like external drives etc ? You have no power leads twisted around anything, which can cause induction? It sounds like you have exhausted most options already. Power supplies do die, so it may be time to return the machine to the maker

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

IMO the problem lies in the USB subsystem of the PC in question.