Do you only get it from the HD DVR, or do you also get it from the DVD player? I'm wondering if it is part of the actual Dolby Digital bitstream or if it's being generated by the 990 or 7500.

From the moment I put the 7500 in my system, I've noticed a soft click from the speakers when the 990 acquires any signal - but I was also looking for it because I'd heard a couple reports of such behavior. It's not what I would consider noticeable enough to be equal to what you mention, but it is independent of the incoming signal format (PCM, DD, or DTS) and it did not occur with my old 750.