Its your receiver, I think. Sorry. I have the same problem with a Pioneer 711. The problem occurs when the receiver switches from a digital to an analog source. That's why you get the noise during the menu on Matrix; DVD menus are often in analog sound, while the movie itself is digital.
Check out this thread (I'm SkunkApe over there):
http://www.hometheaterspot.com/htsth...rue#Post368706
My advice is to return the reciver to the store if you're withing the store's return period. I was too late. I called Pioneer about mine, but they were clueless. I'm too lazy to take it to a service center; somehow, after my phone call, I don't get the feeling they can fix it. I moved mine to the front room for music only, and bought a Yahmaha for movies in the back room.
Good luck. I feel for you. You read all this forum stuff trying to make an informed choice when you buy, then this happens. Darn.