Batboard

I have a 100 watt VHF Maratrac with the older A3 clamshell head. Recently, I started getting intermittent high and low beeping noises when the radio is on. These are the tones you hear when changing channels or selecting a feature the radio isn't programmed to do. This radio was purchased used, was professionally installed, and worked fine for almost two years. The noise is intermittent and occurs regardless of whether the vehicle is moving, or if the wires at the back of the control head are being moved around, or if the radio is in scan or not. I am unfamiliar with the innards and quirks of the Maratrac. Any previous experience with these symptoms? I am wondering about the VCO coming out of lock or some other "computer" error, but that's just a guess. Any suggestions?

TRC