I bought a used EB VPJr online, and it looks darn near brand new. String looks perfect too. But when I step on it all the way, when I hit bottom there's kind of a pop almost like a quick volume jump I guess, just when I hit rock bottom. It makes a noise, I' don't know if I can describe it any better than that. It's super annoying since these things are supposed to be smooth. Does anybody have experience with this? Maybe it's an easy fix? BTW, I looked inside the pedal for the switch to see if I could change the taper (like maybe that would help?) but this one doesn't have a switch I thought they all did? Anyway, I wonder what could be wrong here?