Are you using the iDevice that we sell or a different one? The way ours are wired, the mic in your iPad should be disabled.
And what kind of pickup are you using? I spoke with somebody recently who was having the same issue. They were using a mic blend system and the mic was picking up ambient noise. They blended out the mic signal and they solved their noise issue.
Ah okay, so it's certainly not the piezo. Hopefully you figure out how to reduce the noise. Our iDevice cable is wired to avoid that problem, just in case you cant!