Ok, I'm sorry I noticed this thread just now. I have the same identical problem, and I believe it IS due to the fact that drives are spun down. I can hear them spinning up every time I get a delay in the conditions mentioned by others (pushing the forward button, pausing and un-pausing, or whatever).
And yes, that happens also when pushing the forward button only once. This has never happened before I installed b11, so have been assuming so far that it is a brand new bug. However, this does NOT occur always. I would say 30% of the times...