Welcome to the place. I'm not sure, but some of the PAIA drum machines used a twin t oscillator circuit to create the different drum sounds. The circuits were tuned to a point where they almost went into oscillation. It may be that some of your cicuits need to be readjusted to not oscillate.
Go over to the PAIA site and see if the schematic and user manual is available for download and see what you find out.