[Fabama]

I have owned my pair of Beyerdynamic DT 770 Pro 80's for about a year now, however I have been using them un-amped up until yesterday.
I recently received my first amp and DAC combo (I bought a Schiit Magni and a Topping D20), and I have noticed a bit of a strange issue.
At particular volume levels on the potentiometer (around 7-9 o'clock, a little behind 12 o'clock, and a little behind 5 o'clock), I hear a high pitched noise, similar to the sound of a radio being tuned, and some static.
I want to say that it is somehow related to the USB, as I only hear said noise through the USB connection and not through the optical, but there is something peculiar about it.
The noise is only audible with my DT 770's. I have a pair of Grado Sr60i's as well, and I cannot hear the whining and static at all through said pair.
 
Could it be a problem with my Beyerdyamic headphones? Or should I invest in some method of USB isolation? I had read about the potential of a ground loop, but that seemed to be the case mostly for laptop users, and I am using a desktop.
 
All advice would be appreciated.
 
Thanks.

 

[duncan1]

IF it is as you say it could be the inductance of the earphones along with the resistor and induced capacitance[low value] could be combining to produce a simple "straight"[non-superhet] radio receiver.
           Having repaired old radios for sale -quite collect able here.I have come across this before in audio circuits especially in valve equipment a very low value of capacitance to earth usually cured it/ or even re-routing of wires[change in capacitance of wiring].
           Having said that maybe somebody knows that those earphones have that as an existing fault /or have a more simpler explanation.