This seems a bit of a stretch but since you haven't isolated the source of the problem maybe try switching the speaker cables left side for right to see if somehow you have an intermitent short starting to develop in the speaker wiring or connecting cables and it's affecting a protection circuit in the amp. If the problem switches sides you have a start.
If not, obviously your goal is to isolate their source of the problem. If you have balanced interconnects throughout your system you may be able to carefully disconnect components starting at the Theta transport and working your way toward the speakers. If the noise goes away when you diconnect a component or a cable then you're making progress. Balanced interconnects can also be carefully switched left to right to see if you can get the noise to switch sides.
Hang in their! Remember your experiment is to make only one change at a time.
If not, obviously your goal is to isolate their source of the problem. If you have balanced interconnects throughout your system you may be able to carefully disconnect components starting at the Theta transport and working your way toward the speakers. If the noise goes away when you diconnect a component or a cable then you're making progress. Balanced interconnects can also be carefully switched left to right to see if you can get the noise to switch sides.
Hang in their! Remember your experiment is to make only one change at a time.