Yep, that happened to me, too. Another problem might be the type of wave you choose. If you are using a sine wave to control volume on quarter notes, for instance, then the loudest part will occur on the off beat. This can make it sound as if the sound is canstantly trying to catch up. Try switching to a square wave and setting the offset to its lowest value, see if that is any improvement.

Another thing that caught me was setting the sync value - make sure that you're setting it to "(quarter note)", not "less than (quarter note)."