Brake light on (intermittent) 2001 Windstar LX

My "Brake" light (never ABS light) comes on in freeway stop/go traffic. Slight grind noise at those stops. Light stays on for few seconds after starting to move again. Dealer has checked it out several times and put it on some type scope and finds nothing wrong. Says to bring it back when it does it again...sure, like, I could make it do it or something?

One time while pulling to a stop in a parking lot, not a panic type stop, I hit a tree because there were no brakes at all! Back to Ford dealer I went and again they could find nothing wrong.

Now what? Am feeling totally unsafe.