I brought mine to my mechanic twice and he could not find the problem even though I told him I suspected the half axles based on info I got from this forum and uploading an audio of the sound which only occurred after driving 10 or 15 miles. Sounded like dragging tin cans (ie cv joints of the half axle). I finally bought CVJ half axles from Denver Colorado since I had already eliminated the flex discs (Had them replaced) and found a local mechanic to install the half axles (was a family owned transmission place I found on the internet). He also drove the car and said "nothing wrong with your car"). I told him if you drive it 10 miles you will hear the noise like dragging tin cans. He put it on the lift and turned the axles and said "Nothing wrong". I pointed to the cracked boot and said "Maybe the grease leaked out". Nope. He went to the next cracked boot and stuck his finger in. It looked like it was only cracked but it was cracked open and no grease. And I had no grease on my driveway. See if the cracked boot is really open. You cannot tell just by looking. See if you can stick your finger in the cracked boot. It took me a year to find this problem since I had to drive 10 or more miles for the noise to occur. Since the axles have been replaced I'm driving all over the place with no problems.

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1985 300D Turbo
"Evolution is God's way of giving upgrades" Francis Collins