B 50 audio problems

A year ago I began having audio problems. I would only get the up
sound at 4+. Sometimes, toward the end of the flight, I didn't even
get sound at 5+. The instrument itself tracks the same as the Winter,
and the averager works ( as confirmed by another pilot in the air.).

Additionally, after an hour in the air, the Borgelt ceased issuing a
sound when I flew too fast. (Occasionally it would still emit the
appropriate sound, but there were long periods of silence when I was
flying fast at a low McR. setting.) The associated instrument did
indicate that I was flying too fast.

At this point I sent it back to the factory and paid $200. They said
that there was nothing wrong with the instrument and suggested that I
may not know how to operate it. After using it successfully for 4
years, that seemed like an odd suggestion.

Now I have a new problem. Sometimes when I find lift, the audio is
correct. Other times it indicates a rapidly increasing lift (13+ ave.
and rising) when the lift is 3 or less.

Has anyone else experienced this problem? Does anyone have any
suggestions for solving the problem other than up-grading?