The tiny mainshaft needle bearing can sometimes screech for a few moments on start-up.  Different than what the OP was talking about, though ..

 > I've heard that high pitched noise upon startup, but it
 goes away soon
 > after I start driving.� And I don't hear it every
 time I use my van.� =
 Is it
 > really that bad if it I don't always hear it, and when
 I do, the noise
 > stops within 5 or 10 minutes?
 > Patti
 > 90 Westy Automatic
 > Los Angeles
 >=20