Hi, new AA6 user here... Whenever I patch in an effect pedal in a high gain amp preset, I get very loud hissing. Even if there is no pedal connected to the AA6, (with cables attached to the send & return jacks) as soon as I engage the fx loop I get loud hiss. The cables are all good, and Im using good power. Ive tried all different fx loop settings. Of course this is only when the inserted effect is before the amp block. Any tricks Im missing? Thanks!