Win 7, I7, 16 gigs of ram, sonar X1:
I loop a bunch of soft synths for a couple of measures.  As it loops, it stutters more and more with each loop.  Stop and restart, problem goes away, but starts stuttering again with each iteration. Doesn't happen when I play a long section without loops, but with the same soft synths.   CPU and ram meters are barely budging. 
Any ideas?

What interface and driver mode (ASIO/WDM/MME)?

Never mind, I debugged it by trial and error: it was due to the presence of CW tt-1 in the soft synths.  Don't know why, mine is not to reason why....go figure.

Geoffrey
Win 7, I7, 16 gigs of ram, sonar X1:
I loop a bunch of soft synths for a couple of measures.  As it loops, it stutters more and more with each loop.  Stop and restart, problem goes away, but starts stuttering again with each iteration. Doesn't happen when I play a long section without loops, but with the same soft synths.   CPU and ram meters are barely budging. 
Any ideas?

Hmmm... I know TTS-1 has issues running at 88.2kHz, but other than that should not be a problem.

I was running at 24/44.1.   No clue why TTS caused a problem, but I loaded and unloaded it several times to verify that it was indeed the source of the problem.