I have a Peavey 6505+ 112 combo amp. I do not know much about tube amps, and I have had this amp for about 3 months, and have not really used the crap out of it yet. Anyway, I noticed that when i played any open notes or any riffs with chugging in them, my amp makes a popping noise followed by a buzzing sound that sometimes doesn't stop until I turn the amp off. I looked a little bit online and saw that this problem may come from the amp being placed on the ground roughly, and saw that there may be something loose in the amp itself. I opened the back and noticed that the sound comes even if i don't have a cable plugged in; I simply have to give the top of the amp a flick and it does the popping and buzzing. All I'm pretty much asking is what could the problem be and is there anything I can do about it? thanks