I'm reading more and more about the MT15 hum with nothing plugged in. I returned my first one to the dealer because of this issue and now my second arrived two days ago. It also has the noise although not as bad as my first one. While the amp's tones are amazing, it's not really useable for recording on the clean channel. On the Facebook MT15 group, post after post references the same issue with several others also returning their amps either to dealers or to PRS directly to get fixed. I'm just wondering if there's a known fix at this point before I decide what do next. Thanks.