Sounds like I have had 2 versions of same problem. First the antenna on my '86 735 would over-extend and flop out onto the trunk! Had the antenna replaced at the dealership. Problem turned out to be the bottom of the antenna shaft was continuously forced up/out too far and wore out the knurled stop at the end of the shaft. Must have been a motor sensor problem because now the motor continues to run (loudly) for a few seconds after the antenna is deployed. The garage queen is under cover for the winter so I too will wait for spring to seek solution.