Flapping sound from transmission hump - flotsam on driveshaft?
 

We were on the highway ('96 E320 W210, 180K miles) recently when it sounded like something caught on the driveshaft. Like a fast buzzing flapping that was almost certainly something spinning against the transmission tunnel. Lasted about 10 seconds, abruptly ended (with no change in vehicle speed by me), started quieter about a minute later, then regained its original volume then stopped after 15 seconds or so. I looked back, didn't see the plastic bag I expected to see blowing in the road. At the time I thought a walmart bag was twisted around my driveshaft OR the flex disc (we Alfa owners call them "guibos" which I think means "Doughnuts") was failing and spinning off a tendril, so I stopped and looked under but didn't see anything amiss.
No further syptoms after several hours driving.
Has this happened to anyone?
TIA-
Tom

One day, while driving my 300SE to my car class, it started buzzing like crazy. I pulled over and waitied for a minute or so. There was no more buzzing sound so I went to the school. During lab, I put the car up on the lift and noticed one of my shifter bushings was missing. So I figured it came off and was ground up in the center bearing area and was ejected out the aft end of the tunnel. I replaced the bushings.

Yeah - I had a plastic bag wrap itself around the drive shaft. It made noise for a while. It was bound tight on the shaft and difficult to get off.