The other day I heard a loud noise coming from my 1997 Ford Explorer.
The only way to describe this noise was a loud whining (much like a
weed-whacker at full throttle)  I could not determine if it was coming
from the engine compartment or the undecarriage.

After driving around the last several days it is still happening
intermittantly but I was able to diagnose when it happens. It seems to
ocurr once in a while when I remove my foot from the accelerator.
When I hear the noise begininning it will immediately stop once I
depress the accelerator pedal again.

It doesnt happen every time I remove my foot from the accelerator
(only once in a while).  AC is not in use when it happens and it does
not affect the performance of the truck and I notice no change in RPMs
- it sounds like a rush of air possibly.

Anyone have an idea?