2002 F-150 XLT 4.6L 4WD. Squeaky rear end when starting from stop. Think its coming from the differential. 270k miles. Checked oil in differential...fine. Obvious rotational squeak in center and not brakes. Jacked up left tire and it shimmies (and squeaks) when just letting off the brake at idle (I never tried this before so don't know if that shimmy is normal, little bit of play by hand but I've read that's normal). I've read U-joints can cause this squeak. I've also heard many other weird noises last 6 months or so (grinding and scraping sounds) from this dinosaur but don't have any drivability issues. In last couple years replaced almost all steering and suspension stuff up front and shocks in back. 4WD works fine. Any advice appreciated.

 

It's more than likely your u-joints.

Mark and remove the drive shaft and inspect. Replace the u-joints or buy a new drive shaft.

 

Thanks! I pulled the drive shaft and one of the pivots in the rear U joint barely moves!
Driveshaft squeak (rumble.com)

 

Replace the rear u-joint. It's toast.

 

BTDT, it was the U-joints.