Here in Philly, I am using HDMI to my panel (Hitachi plasma) and DD 5.1 to my receiver. When using the TV speakers and sound via HDMI, on the local ABC affiliate (WPVI) I get random audio dropouts that include a loud strange sound (almost like an electronic buzz sound) prior to the dropout, which last about 2-3 seconds, then sound returns. At the same time, the picture freezes/disappears. My completely untechnical explanation is something isn't meshing with my MPEG4 local ABC channel and the HR20. My neighbor, who still has the NYC ABC feed on his H10 (MPEG2), does not have the same issue.
It's minor, but really annoying when trying to watch a program (non-sports) where dialogue is important. It's the only real problem left with the HR20 (knock on wood) I can see on my specific box. Having none of the other post-update problems (missing partials, deleted shows, MyVOD issues etc.) reported elsewhere on this forum.