I have a QSC PLX1602 that I'm running in parallel mode. I'm using one side of the amp into one cab. Channel 1 works properly for a few minutes but then the volume starts to fade and sounds scratchy until there is no sound. Channel 2 works properly. I bought this amp used a few months ago and have been using Channel 1 into the one cab this way the entire time. This problem just started Tuesday night. I tried different cables and even a different cab. Same problem. Then I tried Channel 2 and that worked fine so I ended up just using that for the night. Anyone have this happen? Any idea what's wrong? Thanks.