12stepper -

I've only had my 990/7500 for a couple days now, so I can't really help solve your problem, but I know exactly what you are talking about. I have Comcast HD cable via a Motorola STB and initially had the same issue when I hooked things up the first time. If I remember correctly, I was initially using analog L/R audio cables from the STB to the 990, along with the HDMI out from the STB to the 990. I recall setting the audio mode for the input channel to 'analog' and then playing with some of the surround formats. I think when I had selected 5 channel stereo I may have had the audio throbbing you describe. Anyway, I have since run the HDMI straight to my TV (don't want to have to turn on the 990 and 7500 just to watch the news, for example) and used a digital coax for the audio and I have no more issues like that.

Anyway, I hope somebody here can get you on the right path. I've still got lots of playing around to do. Auto setup is not working for me, and I need to grab a few more components so that I can hear some really good 2-channel sound, need to figure out the best way to run video, etc., but that will all be another post I suppose.