Hello, I have a Pioneer SX-650 the speakers sound scratchy (checked speaker wires) sprayed cleaner on volume knob no change still scratchy. The thing is when I listened through the headphones everything sounds fine. Don't use that much but was working good every time I turned it on. Same thing when I play cassette deck or phono scratchy speakers and clear headphones. Was thinking the amplifier might be going south but then found it to be nice and clear in headphones. Any help appreciated.