There is a rattling sound coming from one of the tubes (Groove Tube 6550C) on my 300T. It was there when I bought it, and there's nothing wrong with it, but I'm just curious. It only makes a noise when I play an E (any E, doesn't matter which). It's not really a major nuisance or anything, but I just want to make sure the dern thing isn't gonna crap out on me anytime soon or me cause any major damage to it. Thanks!