I have a 1985 300D Turbo Diesel. About 1.5 hours into any trip, a flapping noise starts to occur. If I turn the car off and turn it back on again, the sound is gone and it doesn't occur again for another 1.5 hours. Any suggestions?

I had a similar situation on a 1983 300D,on long runs it would start making noise,I would stop to check it out but find nothing but when I continued the noise was gone!
It turned out to be the right rear axle.
Good luck M.F.

Thanks for the advice about the axle! I will definitely get that checked out. Any ideas how much I could expect to spend on a job like that? I just bought the car about two months ago and every little things keeps going wrong. It has 247,000 miles on it but she still runs/looks great!