Hey guys, I hope someone here can help this is my first post on TGP. Unfortunately, I'm having some issues with a 70-71 Ampeg V4. I just picked it up a couple weeks ago. Worked fine for the first couple hours I played on it. Sounded great. Still sounds great.. but there seems to be some feedback or interference happening. I power it up, play.. 5 mins in and it just starts squealing, almost popping and the best way I can describe it is a feedback kind of sound. If I tap on the top of the head, it goes away, sometimes. Also, the reverb knob makes a lot of noise.. I just leave it at 0. Sounds goes away. But ultimately over the course of an hour playing this noise happens 5-10 times. Sometimes I can tap the head and it stops, sometimes I have to turn it to standby and back on. That usually does the trick, temporarily. Does anyone have experience with this issue? Any help or advice would be greatly appreciated! Thanks!