I assume the unit doesn't feel very hot either?
I find the whole thing strange, 'cause you say that only some patches sound staticy...
If they all sounded staticy, then it would be an output issue, but since some do and some don't it's pretty weird...
I'd definitely take the thing to the shop and have it checked out. Might save your life or an extra 911 call and a visit by fire department (that I'm just joking about).
-ED-