I have an AC15C1 and starting a couple days ago I've been getting this horrible noise like a screeching noise when I turn my amp up past 11 o'clock on the dial, even at low volume I have a buzz that's really annoying. I've tried many different guitars including ones with humbuckers so I'm pretty sure it's the amp. Even with no guitar plugged in it hisses past 12oclock. I'm hoping and thinking that it's the tubes but I gave them all a couple taps and nothing happened, I know this isn't a very scientific way of testing them but I don't have any other way to. The tubes seem to all be glowing about the same. Can someone reassure me that this is just tubes and I'm not going to have to use my warranty just yet, I just got the amp about a month or two ago. Still has the stock tubes. I'm assuming tubes are the problem but I'm not sure, I figure you guys know a lot more than me so does anyone have any insight on this problem?