I had a crate half stack and i was dealing with the same problem.And to add to the problem i ran a boss eq in the f/x loop!!! A noise gate is your best bet in my opinion,the one i had was a dod and it was a stomp box ,so u could run it in the line between ur guitar and amp.dont know if all noise gates are like that but im sure u can find one that will help with your problem.GOOD LUCK.

Wasting no time with the collective 'THEM'.....which dosent include 'US'