The problem is HX Stomp ... my unit I sold, made a ot of hiss in every Fx loop amp in a channel with gain. Of course other units did not make that hiss. You will hear do this, or do that, there is nothing to do, just conecting Hx stomp to a Fx loop in an amp that has a gain channel will make more hiss than most of known pedals that's it ..... Also a M5 or M9 from Line 6 .... I don't know if Line 6 have fixed this with the new units ...