[WarrenG]

Hi:
I had exactly the same problem, both with the Duet and a Behringer X32 Compact. I found that reselecting the interface (or buffer size) "reset" the problem, but it would come back again.

I even completely reinstalled OSX and PT, but still got the problem.

One time this happened was during a bounce to disk, I let it run through to the end (by which time the sound was completely unintelligible) and the resulting WAV was fine. So the problem had to be with the output from the interface.

In the end I replaced the USB cables and made sure both interfaces were connected directly to the computer and since then I've not had a problem.

Hope this helps!