im going to guitar center tomorrow to sell my amp, and now it sounds like ass! i JUST replaced the speaker like maybe a week ago, but after about 10 seconds of it being on, it starts to distort the notes. Is the problem in the head of it? its a Fender BXR 300 C combo amp rated at 300 watts. please, is there anything i can do to get it to be well enough to be sold to GC...i checked my instrument cable and stuff, idk what the problem could be!