Fuel Pump?
 

twice in the past two days after i've driven my stang it has made this weird whinning sound after i have turned the car off. It made this noise for about 2-3 min. then stopped and it sounded like it wascoming from the fuel tank. Could this be the fuel pump about to go out on me or what? And my car is a stock 91 mustang gt if that helps anyone out. thanks
ryan

It is possible that your fuel pump relay sticking on and keeping your pump going. I believe on the 91's the relay was under the drivers seat. Check to see if power is still going to the pump after you turn the key off. If the relay is O.K. it may be the check valve on the stock fuel pump is leaking slightly and causing the check ball to vibrate slightly as the pressure leaks down. You can check that with a fuel pressure guage to see if the pressure is dropping while you hear the buzzing noise.

I hope this helps.