I own a pair of speakers which are powered by USB. I’ve had them plugged into my computer for a long while, but whenever I turned up the volume, I’d hear a high-pitched squealing sound from them which would fluctuate in pitch. For the longest while, I thought this was just an issue with the AUX cable, perhaps something relating to my GPU’s coil whine.
Recently, though, I more or less completely rebuilt my PC minus 1 of the hard drives, which I’m still using now. I noticed that the speakers were still squealing even with the new motherboard, PSU and GPU.
A couple posts I found online indicated that the problem was likely due to an under insulated AUX cable receiving interference from EMF waves.
Despite that, for whatever reason, I decided I’d try to plug the speaker’s power cable into the USB port on my power outlet. The squealing completely stopped! I’m not sure if there is a difference with the power delivered by computers USB ports vs the outlet (Please do let me know if there is!), but the issue has completely resolved itself.
Not sure if this is really the best place to post this, but I just really wanted to tell someone. I’m quite content!
Similar problem is quite well known in sound systems for large crowds (PA): When the source and the speakers share a power source a sort of feedback loop can lead to similar effects, mainly ugly humming. Changing one of the components to a different power source (different phase) will stop the distortion like it did in your case. For PA there are also special filters available for that problem if separate power sources are not at hand.