A couple of weeks ago I bought aforementioned amp. I was very happy with it, no issues so far, but today while playing I noticed a weird buzzing sound that my amp makes whenever I play an A note on my guitar. I tried different fret position, plugging in my other guitar and even moving the amp in case something else than the amp itself was making the sound. Nothing helped. Did anyone else had a similar problem? Any ideas what might be causing it?