I recently bought a 2nd-hand AVR300 to replace my old Yamaha receiver but after I swapped things out I'm getting a buzzing sound from my speakers. I double checked all the speakers connections (+ to +, - to -), then removed all but one speaker-- still got buzzing even when using an input with no incoming audio. I also played with the ground line switch and double checked that the 4?/8? setting was correct. I never had these issues with my Yamaha. I'm going to do some more troubleshooting tonight but does anyone have any ideas on what the issue might be? I'm hoping that its an issue with the connections and not the receiver.