This has been driving me crazy for months. I had a discernible metal on metal squeak coming from the rear, seemingly on the driver's side, mostly heard at low speed. I thought it was the license plate frame or the heat shield around the muffler, but I could reproduce it by pounding the bumper in random places.

The culprit was the metal-to-metal joint of the driver's side bumper support with the bumper carrier. Those two are mated to the wheel well on the driver's side rear with only a plastic expanding nut. I can't believe there was a metal to metal connection (now rusting) and just a flimsy plastic connector holding them together. I replaced the plastic nut with a stainless steel torx bolt and washer (a bit too long) and tightened that thing up TIGHT. No more rattle.

When I have more daylight, I'll put it up on a jack and get more room under there to work, sand the rust, recoat and isolate the parts better. It's SO nice not to hear that dang squeak.

Here's a shot of the temporary fix (fore and aft). The red piece is the bumper support and the black piece is the downward arm of the bumper carrier.

 

You sir, are a God among men.

Did the fix today, used some grade 8 hex bolts I had laying around. No more squeak thus far, and the bumper feels a lot more solid.

Now If I could just get the sunroof rattle to stop...

 

Dear God, is this the answer!? I plan to fully investigate tomorrow!

 

Maybe yes, and maybe no. I've solved three separate rear-end noise problems, all of which became really apparent with the rear seat and shelf out of the car.

The one above was mostly a squeaky metal on metal sound and was solved (as in noise gone). On the passenger side, I have a knocking sound that was due to the exhaust shield hitting the hollow plastic wheel well. I bent the exhaust shield to keep the two away from each other and that noise is gone.

I had another rattling sound that I found was due to the hard plastic edge on the foam bumper insert rattling against the inner bumper skin. That one was my own fault because I pulled down the foam to find the rear fog light wiring and didn't put it back in place correctly.

Now that's THREE separate rear end noises fixed BUT I STILL HAVE ONE . It's a low speed rear end clunking, kind of a hollow sound not unlike the problem with the exhaust shield hitting the wheel well. Not the spare carrier (tried riding without that). I'm hoping it's not the shock tower. Theres a TSB about excess weld metal not letting the shock mount seat flush with the body resulting in noise.