Go to your favorite auto parts store and get a tube (or bottle which will last forever) or brake quiet, or caliper grease, etc. There are about 7 different brands out there, just ask someone in the store. Apply this thick greasy stuff to the BACK of the pad and the pad side of the shim. It should help tremendously. Tracking the car in TX burned (or melted, actually) any grease that was already there, and now you are back to metal/metal contact. Any further high heat braking activity will re-create the problem, just reapply as necessary. Hope this helps.
p.s. Also check your rotors. If there is a small raised lip around the perimeter of the rotors, then that will also cause the noise, although it is usually more of a chirp than a squeek, and will have to be machined out to make it go away.
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Gary Yates
1995 Red/Tan
1992 White/Black
2002 Red and White Cooper S