I just purchased a SHERWOOD RD-6105 receiver this past weekend and have a several problems with it. I had to return the first one I picked up because the AV inputs didn't work and it made a constant low grade high pitched tone when it was turned on. The second receiver I picked up the AV worked on it great, but this one also has the tone coming from both speakers. I did not have this problem with my last receiver. What could be making this problem? Did I buy a lemon or what?
Check you AC ground, make sure your power cable is in good shape and away from all of your source wires (DVD, etc). Sounds like you are hearing a 60hz hum from your power line. Also invest in a good power conditioner. ;)