My '94 940T is intermittently making a whining (sometimes whistling or grinding) noise while moving.It has done this on and off for at least two years.Today,it's back and worse than before.Cooler temps sometimes trigger it.The noise must be in the driveline-it only happens when car is moving;gear selection (and engine speed),including Neutral has no effect on it.It sounds like it is faster than wheel speed.I can't seem to locate the exact direction.Every time I even think of taking the car to a mechanic,the noise goes away!Symptoms point to diff,but why would they come and go like this?Anybody had this? sredwine 940T has 156K,V90 has 94K