Rear end hum when motor is off.

[JarradCUE84]

Hey, I have a problem that is stumping me. When I shut my engine off I can hear a hum coming out of the rear of my expedition for 15-30 seconds. Fairly loud too. What could it be, fuel pump possible? The vehicle is running with no problems at all, but I have never encountered such a strange problem before. Any ideas, let me know.

Thanks.

Sorry, should have mentioned some specs
1999 Expedition XLT
4x4, 5.4L engine
anything else just ask.

[KEITHHATTER]

Does it have rear air suspension? That will cause a little noise.

The fuel pump should only make noise when you turn the key on before starting.

[JarradCUE84]

nope, no air suspension