Hmm.. There's a lot in the signal line that could be causing this (rack, stand, cymbal, etc.). First off I would take the surge cymbal off the stand and unplug it. then give it a shake in a quiet room.. any piezo rattling inside?.. If no, plug it in and test it in your lap (not in the stand). if it's wierd here, try another input (like a tom, etc.) and repeat. if everything's still cool at this stage, I'd say it's either how you mounted it or how your rack is set up..
Let us know how you make out..