The car: 1985 300SD
The symptoms: after first starting up and driving on cold (approx 35 or less) mornings there is an ear piercing whining noise coming from under the car. The noise is so loud that it almost sounds like it's resonating in the cabin. It only occurs for the first few miles and the colder it is the longer it lasts before going away. It only occurs between 35-40mph, any less or more and there is no audible sound.
The background: carrier bearing is new, replaced it last summer when i had noticed that the old one had completely disintegrated the rubber bushing. My first reaction was it had to be driveline related, and since the driveshaft is old i figured maybe the u-joint bearings. But i just dropped the driveshaft today only to notice that the u-joint bearings feel great. Today is a warm day compared to the last few weeks (60s), so i figured that leaving it outside overnight to get nice and cold and then retesting the bearings in the morning may help diagnose the problem.

Any suggestions or ideas while i have the car on jackstands with the driveshaft out?