I've recently bought a pioneer sa 6500 and it was great for a couple months. Recently I've noticed intermittent distortion or no sound at all from both speakers at various times. After checking a few things, I noticed that if I torque the source select over to the left (phono is the far left selection), it fixes the problem. The knob/inside disc trends back to the right if I don't crank to the left. Is there an easy way to keep this from moving from where it should?