one exhaust down-pipe hopping
 

Well, here is the sequence of events, related? I dont know. This is on a 93 300E 2.8. First my belly pan fell off in the back and the screws were gone. So I removed the whole pan until I could make it to the dismantlers for new screws. The next day a truck drops a retread and I go right over it. Soon I notice rattling when the car is in drive or reverse, especially when the a/c is on. Putting in neutral or park quiets it, as does going at a good speed. I put it in drive with the a/c on and put on the e-brake to have a look. One of my down pipes was hopping away, carrying on until both pipes were hopping by the time they got to the tips. I inspected as much as I could without a lift and everything seems to be there and tight. Possibilities: something was knocked off or loose by the retread, or the occurance of the noise and the incident is simply a coincidence. Could bad motor mount(s) cause this? am I doing harm driving her without a belly pan? Has anyone had a similar problem with a pipe rattling?
Thanks for any help,
Brooke

Check your exhaust hangers, the rubber donuts that keep the exhaust up, might have broken one or more. Also check the exhaust mount bushings at the transmission.

Collapsed motor mounts can also cause the exhaust system to hang lower and make contact with structural parts, usually manifest with a solid rattle under certain engne speeds.

Just measure the motor mount to frame spacing [from metal lip on mount].
If it is less than 1/2" [ 13mm], it is colapsed. Common on right side due to exhaust heat....