I am using a Macbook Pro OS X 10.7.5 with 2.8ghz Intel Core I7, and 16gigs of RAM. My DAW is Logic Pro 9. I have two issues that manifest only after a length of time, sometimes 45 mins, and other times more than 90 mins while attempting to use USB for tracking. They are the "vinyl crackle/pops/ticks" and the other phenomenon, is where a 1 second latency occurs. I strum a chord, and I don't hear it through my monitors instantly anymore. I have to close the session turn off the Axe and restart the Mac to fix it.
I can't say with certainty, if simply closing the Logic session and reopening it, would fix it, or if doing that AND restarting the Axe FX II would solve it, but I do all three steps.
I was able to stop hearing bit crushed/distortion by recording at 48K instead of default 44.1K