CAPS Topanga causing noise in my system

[Bigbwb]

Hey guys,

been running a Topanga build with the only mod being a PPA USB card for quite some time. Lately I'm getting a very annoying higher pitch squealing type sound .....not a ground loop hum. It comes through my receiver when using HT bypass mode. The hissing or higher pitch squeaking is audible at my LP. I tried unplugging everything from the Topanga with no luck. As soon as the PC is shut off, the sound disappears instantly. Oddly, the sound is non existent when listening to just my preamp. But when the preamp is in HT bypass, the noise is audible again.

 

Any thoughts or or suggestions to fix this?