Only really noticed this over the past couple of days, but a few sounds such as achievements and some combat sounds seem to have about a ten second delay to them.

I haven't changed anything in my pc or game set up, and it is odd because it only affects some sounds with the majority of sounds playing just fine.

The only thing I have noticed is that it happens more in Stormwind or LFR, so maybe it has something to do with having lots of other players around.