Since you didnt mention it, I am assuming you have tried the "panic" button. Press help, then the right arrow key above the display. This will not fix the cause of the problem, but it may help stop the stuck note.

I have the same question as another ... is it just one key and if so it could be a mehcanical "switch" problem that is released when the poly runs out.

The best suggestion is a tech. Second ask General Music on the Peavey forum if others have had the same problem.