On 100% I also have the sound and freezing issue.
It might be related so i'll share the information : a few years ago someone reported an issue with aof3 (MVS), the issue was related to overclock and it wouldn't disappear when going back to 100% without also removing the related .fs file.
My point is that overclocking once can "corrupt" eeprom files, and it won't go back to normal if you simply set normal clock again.
Imho, setting everything to 200-250% is a mistake, i think only a few games "benefit" from overclocking (mslug2, maybe twinspri ? i don't know of any other game having severe slowdowns on original hardware), and i also prefer keeping the slowdowns of the original hardware (did you ever play the DC version of twinspri without the slowdowns ? It's f***ing hard xD, i'm wondering if the slowdowns weren't there on purpose).