99 chevy tahoe cassette issue?

I have a question for any electronic guys out there. I drive the truck for about a half an hour and then I hear this blowing or electronic motor noise coming from the stereo. I don't want to speculate that it is the cassette player but it definately sounds louder when I push in the flap. The funny thing is there is no tape in the player and it does not turn off with the stereo. The only way to shut it off is to turn off the car and restart it. Then it comes back in the same time. Its a 99 tahoe LT 5.7L with the stock delco stereo. I was also told that it is a cooling fan...does anyone else have this problem and what did you do to fix it?