A few months ago, my SDS-100 began stopping on every conventional channel with a crackling sound, as if squelch (no matter how I set the squelch) wasn't working. Since that began, I have avoided everything except the trunked (mostly P25) traffic, which continues to be received correctly. Is the squelch for the problem channels using completely different squelch circuits, and, if so, does that mean I have some component failure that needs repair? I've had this radio for almost three years. Any suggestions?