I'm just watching "Skin of Evil" right now, and there was a very odd audio problem (actually two within 2 seconds). Just after the away team returns with Yar and Crusher saying that she "needs her in sickbay", Crushers audio sounds badly muffled and extremely low (so low that even turning the audio up I can barely make out what she says). And then it cuts too the bridge with Picard and Worf, and Picard says "go too yellow alert Mr. Worf", and on that line there is an odd doubling effect on his line. They're both in the center, but one is just slightly delayed, so you get an echo. These ar errors from the 1980's and not errors from 2012.
Edit: I just checked the original audio, these problems are in the 25 year old audio, but the levels on the audio surrounding Crusher's line are mixed lower too match, whereas on the Blu-Ray the surround audio is mixed higher; Picard's doubling is also in the original audio, but not as noticeable.