I have a B-52 AT-100 tube head and for a while now its been making this wierd sound, almost like a static, sometimes it does it for just a few seconds, and other times it will go for about a minuet. Sometimes after it makes the sound, it alters the tone of the gain channel, it sounds like all the mids are completely gone. I got all new cables(good ones monster and planet waves) and it hasnt helped the problem. Maybe I need to replace the tubes? Ive owned it for about two years and it has the same tubes as when I bought it. Any help on how to fix this problem would be greatly appreciated as I love the tone of this amp and don't want to(and cant afford) to buy a new one at the moment.