Hey everybody, I have a 70's era Fender Bassman 70 head that I have set up with a 15 inch Carvin cab. I let the head warm up a bit plug in and play and after about 5 mins I get a loud buzzing sound that comes out. Not a feedback noise, just a loud buzz that no matter what setting the volume is at, its always louder. Turn off the standby switch and goes silent, wait a few minutes, turn it back on and I'll play and it'll do it again. Any ideas?? Thanks in advance for any feedback.