When does it squeak? Have you considered a faulty rear wheel bearing? Is it coming from the drivers side? My car has 80,000 miles on it and, I had this squeak that was driving me nuts. Put the car up on jack stands to try and figure it out but could find nothing. Turns out it was the rear wheel bearing.
I could only hear it sqeak at very low speeds, I mean like pulling away slowly from a stop sign or something, it sounded like every rotation of the wheel there was a slight creaking noise. I found out what the problem when I pulled off the rear caliper to change the pads and I noticed all kinds of play in the rotor. I'm talking like a full 2mm in each direction. It was REAL bad! I'm actually still in the process of changing it, it's a real pain in the ass.