Problem with Bose 321 System

[W1UJR]

I have as Bose 321 system on the bench that has the following issue:
1) After extended use the audio becomes very bassy and distorted.
2) By plugging and unplugging the DVD unit from the large base unit the sound is restored.

Is there a common fault with this system, a pattern failure?
The problem has been occuring with more and more frequency, but is difficult to simulate on the bench as the powering down and then turning back on corrects the problem for a short time.

Suggestions?

Tnx - Bruce