distortion from my Aguilar OBP-2

[Reynoldbot]

I recently had an Aguilar OBP-2 preamp installed in my Fender Jaguar, and I've been noticing some light distortion coming from my bass ever since. When I turn the preamp off it goes away, and predictably the farther up I turn the bass/treble knobs the worse it gets. So does anybody know what's causing that? How do I fix it?

Thanks!

EDIT: I should also mention that the battery is brand new. I'll replace it anyways just to be sure.