From about 35 mph and up, I get a whirling sound from the rear of my 03 Supercrew. The funny thing is that when I let off the throttle it quits, and if i tap the throttle, the whirling sound starts then stops right away!! There is no vibration that I can feel. I think it is the something with the rear driveshaft or the rear diff. My truck has a 3.73 Limited Slip gear. I wanted some opinions from everyone before I call the dealer for warranty service. Please help!

 

you have just been offically initiated to the FORD REAREND WHINERS CLUB
your rearend will have to be rebuilt. mine is doing the exact same thing but i also have the vibration which the 4x4's have that go along with it. not exactly sure what they will replace but i know the are replacing the clutch packs along with the bearings and hopefully the gears. go to your dealer, they know there is a problem. not sure if they figured out how to fix it permanently thou.

PS. make sure you check the inside bottom of your doors (and tailgate) as well. Rust will settle in where the outside door panel is rolled over the inside panel. nice quality design, no sealer was used at all. i have had mine oil sprayed before the last 2 winters and i just noticed yesterday there was surface rust started. i'll have to show that to the dealer when i go in on Monday still love my truck thou.

 

It's a commonly reported problem on the 9.75" rear ends. Generally, Ford will give one of several BS evaluations and start throwing parts at it, with varying results. After 2 trips to Ford for my 2000 9.75" LS without satisfaction, I tore mine apart myself. I found the pinion depth to be off. I threw some 4.10s in and properly shimmed the pinion and the noise stopped. Good luck and stay patient.