Now I *really* can't notice a pattern. Over the last few days I did a fair
> bit of driving and sometimes it didn't do it at all when the car hadn't been
> driven for a while (had already cooled down), and then sometimes it did it
> if I backed up *immediately* after having driven the car for an hour on the > highway...
This squeaking was happening to my '92 XLT and it turned out to be the rear drum brake shoes were ratcheting out too far and pressing against the drum because of using the emergency brake . The rear brake shoes cracked due to excessive heat build up from continuesly rubbing against the drum. I replaced the brake shoes and adjusted the brakes and have not used the emergency brake and have not had any problems with the squeaking since.