> Is there an option in MAME that can circumvent this somehow? And why doesn't it > happen if the game is set to less than 60Hz?
MAME attempts to auto-compensate for minor drifts, but it stops short of creating audible pitch distortion (which making the audio frames too far out of sync with correctness would do). Depending on which way things are drifting it's quite plausible that it's able to compensate in one direction but not the other.