If both channels have the same problem, yes. Example; Maybe there are two components on one heatsink that have flexed and broken traces at the same area on the PCB. 12voltvids on YouTube has many examples of this type of thing. May not be your problem, but worth it to look.
I looked around but there are no heat sinks other than the case it self. I've ohm'ed out the feedback circuits and have continuity throughout. Flexed board a little but no changes were seen.
I set up this part of the circuit in a simulator and it shows the 1k ohm resistor I have installed in series with the source leg of the audio FETs will prevent sufficient feedback. However if I connect without the resistor, the FET overheats and shorts out very quickly. Kind of a catch 22 situation it seems.