I'm not sure I hold much hope for swapping the regulator as I can't see how anything on the coil side of things could possibly get into the audio chain.
Having now proved the amp is silent I would next connect just the audio grounds to the board leaving the signal input and output points not connected and now see if it is still silent. It should be.
Having now proved the amp is silent I would next connect just the audio grounds to the board leaving the signal input and output points not connected and now see if it is still silent. It should be.
Do you have digitial multimeter?
Can you provide clear pics of the PCB traces on the bottom of the boards?
Also, pics of the tops of the PCBs so we can read part numbers on the various devices?