I've watched 2nd part, but I spotted something in 2:39 in this part. Noise seemed to be periodic - I think it might be some coupling and heterodyning with other periodic signal - clock or dc converter ripple, maybe on digital side. It will not be handy, but maybe some off-circiut check of decoupling capacitors?
For 2nd video I'm curious about negative voltage on broken diode vs. positive on operating channels - but this wouldn't be issue IMHO. Dave, have you checked voltage on pads after desoldering diode?
Last thing - maybe some phone procedure (factory reset, reflash with newest firmware, if available and recalibration) will work?
Good luck!
Karol
Edit: I mean heterodyning sample clock with ripple or other clock.
Karol