Very odd that the same problem would happen simultaneously on all channels, considering each channel has its own power supply. Perhaps there's a power-on muting circuit that's sending garbage to all channels?
Sources/processing: stack of stuff that if it isn't vintage now, it will be soon!
Amps: stacks and stacks of old iron
Main speakers: big DIYSG
Surrounds: Bose graveyard
Subs: a bunch