If it is repeatable with certain songs then check the source, i.e. CD's or records...as for components, it might be a driver in the speakers, or mylars with push/pulls....then tighten the screws / bolts first.
Neither the Pass nor our amps have that kind of intermittent problems, and they don't have "muscle memory" .... .
it would either distort or it doesn't in either case.........