I have a 12V portable box fan that is acting funny this spring. It will run fine for a few seconds, then slow to almost a stop for a few seconds, then pick up speed again. It does this in both high/low speed with the slide switch, and both battery/wall transformer power. I have found than when the motor slows the voltage to it drops and the two resistors in the circuit become hot. The wall transformer also becomes hotter than normal. My only guess is that there is some sort of short in the motor even though it isn't getting hot. It also turns freely by hand so it isnt seizing. All connections seem good. Any ideas?