I picked up a new GK MB115 combo a few weeks ago. Love the tone, the weight and the features. But shortly after I bought it, the speaker started buzzing (I don't mean the grill was rattling). It increased as I turned the amp up and was more noticeable on the deeper notes. I double-checked all the screws on the speaker and made sure they were all tight. Eventually I just went back to Guitar Center and told them I wanted a new unit. So they ordered it for me and I just made the trade last night. Playing the new one in the store and after I got it home, I was thrilled that there was no buzz. I assumed the first model I got was slightly defective and looked forward to many hours of buzz-free playing. Well... Got up this morning, turned it on and what do ya' know? The buzz is back. Just as bad as it was on the first amp. I haven't even pushed it hard yet - kept the volume at about 9 o'clock and both the gain and boost at 2 o'clock. The only thing I can think of is that leaving it my slightly moist and humid basement overnight did something to the speaker? Please help me, guys! I'm going to leave it upstairs in drier air for a few days and see if that helps, but if not I'm guessing I'll have to take it apart and look at the guts. If anyone has any expertise they'd be willing to share, I'd appreciate it!