Welcome to Ford radio... it's the nature of the beast. My '88 and '95 Fords
both did the same.

My '99 F150 did it so I popped the radio out, opened it up, and found a surface
mount component was loose on the circuit board. A quick resolder job and
everything has been fine ever since. Couldn't tell you for sure if this is the
same problem on yours and I can't recall exactly the part number or where it
was located on the board since it has been 3 years since I fixed it but that is
what I did for mine. That type of soldering job isn't highly recommended for a
novice so if you decide to have a look for yourself and you do find the same
problem then make sure you get someone who is familiar with soldering practices
to do the soldering part for you.

Cheers,
Lawrence

There is a guy in NY who fixes it for about $50.  After shipping and all you
are probably looking around $75.   I still have mine but I didn't get around
to doing the fix because I didn't want to be without a stereo for a week.  I
ended up getting a $100 after-market Sony cd player (for an additional $25
it will play MP3's if that is your thing) at Circuit City that took about 20
minutes and $50 to install.  It sounds better than stock, has a removeble
face and AM reception was greatly improved.

Shine a flashlight in the display and see if you can read the numbers. Lots
of Ford radios have a light bulb that back lights the display. If the lamp
goes out you can't see the display.

Al