Need 302 help

I have a Cambridge 302 that, until 4 weeks ago, was working fine.

Now, at power up, it seems to calibrate the needle just fine and then, after a few seconds, sends the needle sweeping around with a buzzing or clicking sound. It does this a few times and then settles down. Curiously, the circling graphic is illuminated after the needle calibrates.

In flight while thermalling, the 302 works great, both vario and averager, and agrees with the mechanical vario.

In level flight, it is possessed by a gremlin. The needle swings wildly and the audio follows. The speed to fly graphic is way off - indicating "slow down" even at very slow air speeds. However, the vario graphic seems to be reasonably in line with the mechanical instruments. Thus, the vario needle and sound seems to be independent of the graphical vario read out.

I've checked the settings, the polar, and the power supply. All seem to check out fine.

The 302 and 303 units were rebuilt at the factory by a prior owner in June 2012 so I believe I am dealing with a new problem.

Any advice would be greatly appreciated!

Lou