I have a PSR-600 that is several years old (I bought it used through RR) that recently has started to do something really annoying. The squelch will either stay open after receiving a transmission or sometimes just open up, with the squelch roar. Adjusting the squelch knob does no good. I tried it it the house on AC power and in the car with DC power. I tried on several different kids of antennas. Running out of ideas... The thought I had is that that PLL (Phase Loop Lock) isn't working right which makes me think the radio is toast and I'll have to buy a new one. Any ideas?