I too, have had this happen.
It doesn't happen often, but I've found that simply cycling through the sources fixes it. In my case, I go to tuner, then aux, then back to player, and everything is fine.
Personally, I've only ever had this happen when running with the Hijack kernel, but that's not to say the problem isn't present with the standard kernel. I guess I just haven't run the standard kernel for long enough to tell.
What kernels are others running who have seen this problem? It would be nice to tell if it is a problem introduced by the Hijack kernel, or whether it is a problem in the standard release. Personally, I think it could be related to the voladj stuff in the Hijack kernel, but I can't be certain.
Andy.