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Does this only happen if you are coming to a stop (vehicle moving) and you step on the brakes, or any time, including if you're already stopped? Does your 1994 Explorer have ABS? Is the ABS light on? Does the ABS light work?
It sounds like the ABS is activating as you come to a stop, explaining the feeling in the pedal and the noise. There have been a lot of posts about folks replacing their rear ABS sensor on the rear differential to fix ABS problems which may be a route to go if you are in to shotgunning parts. If you want to have a good feeling that what you're replacing is the problem, you'll need a scan tool that can access the datastream of your ABS system and monitor the wheel speed sensors real time to figure out which one is reporting a speed inconsistent with the others. Then inspect that sensor, tone ring, and wiring for issues.