I've been loving mt TAFM and the sounds it can make. Playing it today it started to make a loud, low frequency rumble or hum when I engage the pedal. While playing through it it sounds fine but just turning it on makes this sound. I tried running straight through guitar>TAFM>amp...same issue. It has isolated power. Opened her up and don't see any obvious issues with the wiring.
Anybody had this issue? Ideas about what it could be?