A bad resistor in the power supply can cause the popping sound you mentioned hearing at night some amps will do this when there are issues in the power supply. If the manufacture would of had speakers hooked up to the amp they would have heard this the first time it was on their burn-in rack, they also should listen and not just take measurements.
This time around i'm sure they took their time and fingers crossed all should be good.
This time around i'm sure they took their time and fingers crossed all should be good.