All of a sudden my 500-C is doing this thing where it will suddenly in one channel get really loud and trebly. I think it's only in Phono Stereo mode. If I turn the volume knob really fast back and forth it goes back to normal. Does this sound like a case for Deoxit in the volume control? The only changes I've made to my system are to install a moving coil cart in my turntable (but I doubt that's the cause), and to change the cabling into AUX and Phono Stereo (I hooked up both AUX and PHONO cables at the same time so I can simply choose on the 500-C which input source I want to listen to using the SELECTOR knob). I've tried jiggling the cables which does nothing. It won't do it for days and then will maybe do it several times during the night.