I have a tele with a fishman piezo and preamp in it. Whenever I turn on any true bypass pedal it's plugged into, I get a fairly loud pop, and it's every single time I engage the pedal. I've had pedals in the past that pop the first time you engage them, but that isn't the case here. I have another tele with a graphtech ghost system with preamp, and that guitar never pops with the same pedal setup. None of my other guitars do either.

The piezo and magnetic signals get split in the preamp and sent out separately over the 2 leads of a stereo cable. One lead has 3.7v dc if I measure the ground and hot for it, and the other has .06v dc on it. Pedals pop whichever side they're hooked up to.

Any ideas? I'm not supposed to have DC on the outputs, right? Insufficient ground for battery? Short in preamp?

Thanks in advance.