Whining noise
 

What is the whining noise when you turn the key into the "on" position on a 97 mustang gt?

The fuel pump will whine for a couple of seconds when the key is put to the on position. The noise will be louder when you get closer to the tank. It is the pump building fuel pressure to the start/run the car. All cars will do it, but how much you hear it will depend on the type and brand of the pump as well as the physical position of the pump in proximity to the passengers.

Thats the tires, they know whats about to happen to them..... or the fuel pump as stated above

Mine is very loud. I'm wondering if it is going to go out soon...

Could the sound be affected by how much fuel is in the tank? I'd think maybe the less fuel, the louder it would sound.

Yeah, it could. In my experience it is not an enormous difference though, hardly noticeable .

Most likely the fuel pump, notorious for mustangs, but honestly harness that sound! let your fuel pump pull a prime and then fire that puppy up! Greatest sound ever!