Hi everyone, so I recently purchased a Marshall Code 25 off of a friend and the amp is perfect for what I need; however, every now and then it starts buzzing out of control. I'll turn it on in the morning to start recording and the buzz is so loud, it almost overpowers my guitar sound! I have tried 3 different guitars, acoustic and electric, bought a high-end Ernie Ball cable and even moved house and the buzz is still there! I was able to fix it in the past by updating ad overwriting the firmware and then leaving it unplugged for a few hours to a day and that solution worked for a long time, but now it's buzzing again and nothing I've tried has made any difference. Another thing, its plugged into the same power strip as my PC and monitor, but the power strip I've switched to is a $50 uninterruptible machine of a power strip that looks like a space ship, to no avail. Also, when I turn my amp on, it makes my PC monitor kind of short-circuit and the picture freezes and fragments for a split second and then goes back to normal. I have tried every possible amp setting, and only setting the noise gate to 80% gets rid of it, which is unusable. I have also tried other power outlets and it only works when it's in a separate part of the house. I should also mention that the sound does go away when I turn the preamp button off on the amp, which again, makes the amp unusable. The house I moved to is also relatively newly made and has had various electricians here to sort out any previous power issues in the past few weeks. I'm at my wit's end and I seriously need some help!