[harsh]

Doesn't anybody elsehere ever use the SD outputs of their 921?

I've done it once to dub off an OTA HDTV program to VHS (the results were not great), but I'd expect that it is quite uncommon to use analog output with the 921.

I wonder if you might not be having some sort of power, heat or grounding issue that is contributing to this problem. Is your 921 enclosed in any way? Do you have a keyboard connected?