Loose Object in Underbody of W124

Hello everyone,
It appears my 87 300D has a gremelin -- a loose object somewhere in the underbody of the car. I believe it to be a socket I may have left on the battery tray,
as a couple of weeks ago while pulling out of a gas station, I heard a drop and ka-thunk which I thought was my gas cap, only to find nothing amiss. Soon after, when I took a corner or braked/accelerated with decent vigor, the loose object would roll around a bit then hit somehting and stop until the reverse motion was applied... in which case it would roll the other way until it hit something.
I removed the noise encapsulation panels and found nothing, the noise persists. The sound seems to come from (and sounds just like) something moving around in the passenger door map case, but when you sit in the passneger seat and hear it, it's definately under you. It rolls as far foreward as the front axle/wheel well and stays confined in the passenger half of the car. It rolls as far backwards as under the rear passenger side seat.
Any ideas on where this bugger could be hiding, and how to get it out?
Thanks in advance! Mike
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