I use AA2.0 and my rig usually has little or no lag. When I hit play or record it starts immediately. However, I have had times where, for example, I muted a few tracks so the artist could experiment by recording newer ones. (Instead of pulling the old tracks out of the multitrack I just left them in there because I didn't know if we would go back to them.) This sometimes causes an unexplained lag of 8 to 10 full seconds before play begins and I start to notice small pops, clicks, and jitters once in a while too. I later discovered that if I pull those muted tracks out of the multitrack, things speed up again and the clicks stop happening.
Weird!
Also temporarily locking some tracks that have effects on them can help take some load off of your processor. Worth a try.
RawDepth