Diesel backfire?
 

85 300d that runs fine unitl 45 min to 1 hour at highway speed, then emits a slight chirping sound from the front (like a fan belt, but they check good) and a rumbling underneath that sounds and feels like exhaust noise/pressure. The rumbling increases in intensity when gas pedal is disengaged and the noise rumbles on all the way to a full stop (toll booth), at which point the car fixes itself and drives without problem. The only way to fix it is to come to a full stop, slowing down does not help. I can't take it to a shop unless I can find a mechanic that wants to ride with me for an hour. Can anyone offer any advise?

Thanks,
Clay

I'd check the rear end and look and see if the axle half shafts are loose.

Thanks, I will check the rear. I also have noticed a miss at idle and that lead me to check the injector lines. I found one wet with diesel and will replace it today if I can find the right line. I still don't understand how it would wait 45 minutes to give me fits but I'm no mechanic.

Clay