Hi, Got a used F50 combo; "slightly used" ?? I actually love this amp; my guitars sound great thru it ! Only problem is ,that 'hiss' you would expect when an amp is on/vol. up , seems excessivly loud. With vol. & gain set at 1/4 it's quite noticable. Is this normal ?? Any ideas ? Thanks, Rich.. 2) Tubes are OK; checked them. Talked to Mesa;said some of this noise is normal..I noticed when I hook up my effect rack in the loop & mix 90%; noise goes away.So does it have to do with the effects loop ?? Should I try connecting the in & out with a patch cord/will it harm anything? Leave rack hooked up?/ any suggestions ? :roll: Rich..