First, let me say, I hope someone can be of help, I just signed up. I ordered a refurbished Onkyo TX-SR503. It seems pretty good I guess, but in the rear surround speakers there is noticable hissing when I'm watching a movie and there's no sound going to them. When sound comes from the rear it's ok, but when there is nothing, it's annoying! There is more hiss in the rear than the front. I switched around my speakers and wires, but it's always the rear channels that do it. It isn't loud, just noticable. Is this normal for a lesser expensive model, or should this not be happening? Thanks a lot!