I had the “pop” issue with my fbv and spider v 60. I bought both at Sweetwater, It happend with the loop function. When id played back the loop it would pop at the point where i stepped on the function switch at the end of the loop. I went back and forth with the tech at sweetwater. Tried changing cat 5, updating firmware (prior to release of MKII) tried grounding fbv (thought it might be static electricity) but nothing worked. Sweetwater was great and exchanged the fbv. However The new one popped once but now has not for a long time, which makes me wonder if or was something it was something with the amp. I didnt try checking the pins as suggested bt fflbrggst. Maybe a possibility. ( thx for the suggestion) tech at Sweetwater told me he took the fbv apart, checked solder and switches etc. they hooked to spider v 60 and it popped for them too. They too are stumped. They could not find anything. They actually sent it back to Line 6 to see if they can find it anything. Tech told me hed let me know if they tell him anything. I’ve updated the firmware again to MK Ii and so far it has been OK but I don’t know if that has anything to do with it.