2001 tribute with about 100K Kms. Recently, when driving, sometimes we
hear a whine that goes up in frequency (to about 3000Hz--wild guess!).
This whine stops suddenly when I touch the brakes. There is no
discernible change in the efficiency of the performance of the vechicle.
 On a 5 minute drive last week, it happened about 5-10 times. Each time
it stopped when I touched the brake pedal, but recurred moments later. I
haven't heard it since.
Any ideas?