I purchased a used Mpulse 600 on Reverb. When I opened it out of the box and hooked it up to my Fender 610 pro Cab I was blown away by it. It is a tone beast and I can see why it is highly regarded on here. I noticed two of the EQ knobs were scratchy , but I fixed that right away with some electrical contact cleaner. The main issue with my amp is that when plugged into the active input ( with my Peavey cirrus and Ibanez prestige active basses) it works for about 10-20 seconds and then it gets a loud popping, scratchy, ugly sound.. on the active input it is unplayable. The passive input seems to work fine. This is the 1st gen model with the two separate inputs ( no switch). Can anyone guide me in the right direction as to what to do to fix this issue?