Trying to eliminate a very annoying 120 hz (I think, seems higher than your typical 60 hz hum) buzzing sound coming through my setup. I’ve tried tons of things, new surge protectors, different outlets, hum x, etc. it’s a buzz that come on every 6-8 seconds, buzzes for a few then goes off, never stopping. It does disappear on occasion and other times it’s less pronounced. Its not the amp, ruled that out long ago.

My setup is very complex.
Ascend speaks obviously
Yamaha cx5000 pre
Parasound amp a21
Parasound pre p7
Behringer fbd
Dual subs Rythmik
Custom built pc for streaming movies and Jriver music with 200 watt external power supply (hd Plex)
Schiit dac
Directv box
Sony ps3
Outlaw 7 ch amp for surrounds and zone speakers

I’ve tried unplugging cables many times and can’t seem to locate the root of the problem.

Any suggestions on where to begin?
Thanks.