Hi, I recently got a Mesa D-180 tube amp, similar to the 400 and 400+. Vintage '82, no graphic EQ. I love it! One thing I've noticed -- there is a faint static noise that accompanies notes (i.e. goes away when nothing is being played). It seems to be heat related. The amp has a 3-position fan switch: off, low, high. If I leave the fan off, the static gets worse. When I switch the fan on, it seems to go away. Another clue: When I first go the amp, I played a rehersal with the fan off. Notes started to cut out after the first couple of songs. I switched the fan to high and have since not had any problems. Any ideas? Pete P.S. Anyone know what the toggle switch on the far left of the back of the amp does?