I have A GK Goldline 500 bass head that powers a Hartke 4x10 cab. I haven't played in about 4 months, but plugged in last night. I had it set up without any effects in the loop. Head to cab, bass to head & I was getting a distorted sound that was crackling & also fading in & out. When I plugged in using my pedal board, using the send/return, everything played fine, no problems. Anyone have this happen or might know what it is? Effects loop-plays fine. Direct input-not fine.