I have to share this story. I was driving my 1980 300SD down the four lane
at about 65 when a loud WAAOOO--WAAAOOOOO sound started from the car
sounding like a puppy in pain. OH NO, I thought, the tranny is going! Or is
it the turbo? I slowed down and the noise stopped. Well, it must be the
turbo. The sound happened a couple more times before I got home at various
speeds and I was then sure it was the transmission or a bearing at the rear
of the engine.
When I parked the car and got out the mystery of the noise was immediately
solved! The chrome moulding around the front window gasket had become loose
and the wind and molding were making the howling sound!