Problems with my Novation drum station

[unander]

I've just bought a used Novation drum station in order to produce the old TR808 and TR909. The module works fins, except one frequent problem: sometimes the drums gets distorted and I hear a strange fuzzy sound in my monitors, it slowly increases in volume but after a while it slowly disappears again.. this happens about once a day, I've checked all my cables and volume-settings, but the prblem seems to be the module.

Thanks to any information, help or tips!