Hi, just tried out my new SV20H head for the first time, running it through my fender 4 x 12 cab (8 ohms). Sounds awesome but I noticed a slight hum when the effects loop is activated. I was running a solid gold FX surf rider through the loop but it did the same with a Boss Space Echo as well. I also took the pedals out of the equation and just connected both send and return with a single jack cable and it still happened. It isn't a loud hum at all but I'm just checking if this is normal? My Origin 50 head that I have been using for the past year didn't make any hum at all with the same pedals!