I have a Pioneer reciever and, sometimes when it switches between Dolby Pro Logic II and Dolby Digital (every time i pause then play a DVD, every time I turn xbox on), it makes a loud scratching noise through one of the the speakers, but its never the same speaker, and it only happens when Dolby Digital\Pro Logic II is involved. Sometimes it makes a high pitched wailing noise. It goes away when i change the input then change it back. Does anyone have any idea whats wrong? It's a Pioneer VSX-D711.