I was in the process of swapping transformers and it didn't fix it.

Then with transformer on the floor (and powered)

I bumped one of the cables feeding speakers and it stopped !!

Then I just kept wiggling stuff until I found a bad connector (on the board).

If it were me (because I like dabbling in this stuff and comfortable with high voltage). We work with 30,000 volts at work.

I would either pull transformer plate and start wiggling stuff that I can reach or try swapping transformer plates between the two and see if problem moves.

I don't know how an 8K is setup in back. But you may have to remove whole back plate(s) to find it. To send in for repair you may have to do that any way. But be really careful.

- Fiddler (IMHO)

If you think listening to music is fun, try learning an instrument.
HT: G61RSL, 4x5K, 5.5KHC, 2xSC6000, Transporter, HD621, Philips BDP7501 4K, Tivo, 65" LG OLED 4K C6
Computer: Foobar2000, 5K, Mojo, HiFiMan HE1000 V2