Yesterday I was giving my "new" amp it's first truly extended workout since I serviced it a week or so ago. I was hearing some strange "ghost" notes or something I can't fully explain, especially on higher notes on the high E string. I thought maybe there was something wrong with the tone stack so I tried the other channel (non-reverb and vibrato one). Same thing. Well, maybe it's fret buzz on the higher notes. Got out a different guitar, same thing. Something wrong with the speakers in my 2 x 12 cabinet? I was sitting in a chair about 10 feet from the amp, at about a 45 degree angle to the speakers. So I get up and move closer to the amp and I no longer hear anything out of the ordinary.
Well, it's been unusually hot here, and I had a box fan sitting on a chair a few feet away from me, more or less right between me and the amp. When I turned the fan off the weird notes were gone!. Somehow the higher frequency notes travelling through the fan blades was doing something to the sound waves, and that mixed with the direct and reflected sound hitting my ears was causing this weird effect. I'm glad I don't have to tear into the amp so soon after completing the service. Just move the fan, lol.
