I am working on a c-300 chiro audio amp, I noticed one of the channels made a really loud strange noise from the speaker (like a cap discharging),, I turned it off asap, I put a meter on the rail voltage on the output pcb + an - ,,,, Im pretty sure I was missing the - voltage,,, I pushed on the pcb an it came back, dont know for sure if my meter connection was bad or what,,,, just wondering what would be the effect if I was missing a - rail voltage to the outputs (in general)