noise from '90 200tqa

[Nick Lawrence]

This is a multi-part message in MIME format.
--
[ Picked text/plain from multipart/alternative ]
Vehicle is '90 200 tqa with 162k miles.
The noise is a whine or moan coming from underside in the middle I think. H=
appens when car is moving, changes sound only slightly with speed change, b=
ut only audible 'till about 45mph.  Not affected by load or whether car is =
in or out gear.
Not always present.
It did this noise last spring for a short while then gone for several thous=
and miles.
Any suggestions?  What noise may come from the center differential?
TIA
Nick Lawrence
--