I have a denon av1905 (full kit list in sig) and tonight i noticed it's making a very high pitched beeping noise. i've tried all types of output stereo, 5ch stereo, DD, DTS etc across all the various inputs and it always make this noise, i even get it when i use headphones. it sounds like a feint alarm going off in the distance and is just the right sound to give you a pounding headache in a minute or two. i'm at a total loss as to what may be causing it, any suggestions on the first things i should try and rule out? thanks in advance.