Thanks for the tip on the ground loop isolator- I'll check it out today!
RE: the comp video inputs- I have an Oppo DVD and the HDTV box feeding into DVI 1 & 2, but also have a Sony DVD player in the system that I mainly use for CDs, but do occasionally also use for DVD- I can't get the 990 to accept/display the DVD/video when using the Sony's component output, even when the video input is set up correctly on the 990. In the course of trouble-shooting the ground loop problem I also tried to use the comp vid input from the HDTV box, but again couldn't get the 990 to display the video- I'm using the 990's DVI output to feed all sources to my Samsung HDTV...