something in the (rear) drivetrain is squeaking when I back up

I have a 2009 Toyota Tacoma 4x4 4.0L.

When I back up, I hear something squeaking. It almost sounds like a mouse using a hacksaw, if that makes any sense (sorry if it doesn't). When in drive at a low speed, I can still hear it a little bit, but it's greatly diminished.

I tried greasing all three u-joints. That did not help.

I'm thinking carrier bearing?

...although all carrier bearing Googles seem to point to more of a grinding noise or a vibration as opposed to a high-frequency squeak.

Any ideas? Thanks for any help!

 

Could be the leaf springs.

 

I'd remove the drums and inspect the shoes.

Also check your leaf springs for breaks.

 

When you greased the universal joints did you get grease forced from all four bearing caps?

You may have one of the grease channels blocked by rusty bearing debris.

 

Squeaking in reverse is almost always u joints