There are known issues with WAV playback in LÖVE as of 0.6.2, because we use libmodplug for WAV decoding and it doesn't seem to really work all that well. I don't know where the fault lies in this case, but libmodplug is definitely much better suited as a tracker player.
I propose we switch to another library for WAV playback. libaudiofile looks promising (and adds AIFF support) but doesn't look to be able to read from memory; I'm not sure how to do that with libsndfile either, plus libsndfile has issues with compiling Universal binaries on Mac OS X. Anyone who can come up with any alternatives, please suggest them.