Loud crackling noise when set to some functions

My Denon AVR-3805 started making loud "crackling" noise (thru the speakers) when I set the Function dial to just about any source (including TUNER) except for DBS (cable box) and DVD (e.g., even input source settings that do not have equipments connected to them like PHONO). The crackling noise is also heard when I set the Function dial to the V. Aux Input on the front pannel. I also hear the crackling noise when I set the Function dial to DVD while the DVD player is turned off. The crackling noise will disapear when i turn the DVD player on.

I first suspected that my speakers were the cause, but i can hear fine from both of the speakers when i am watching a movie on the DVD player or watching cable content.

Any idea what might be the problem? I appreciate all the help I can get.

-- Haytham