I'm not clear on exactly what your problem is here from how you phrased things. Is this with all dvds? I get this with a few specific titles (like Dinner Rush, a fave of mine, i put down to badly mastered disk). I suspect so but worth asking. And you say you replaced the drive, so the new drive does the same? Or do you mean the old drive does the same on other machines?
Also, for most effective help its worth giving more details. It the imac G3/4/5/intel? Sys version and ram? Playing though DVD player or other app? Internal speaker or external? etc etc