Something fell off??

Had a tire rotation today, drove home & parked in the garage for a few hours before taking my wife to the mall.  When I came back & opened the garage door, there was a small black piece of plastic laying on the garage floor where my Hummer resides.  It's a "semi-circle about 2" across & 3/4" tall.  It also has two tabs (one on the base of the round side & one on the base of the flat side).  On the inside center of the part is the number 4.  There is also a stamped A.M.A. in one section, a number which I presume is a part number 031D0380 in another section & finally the letters REV. in another section . It appears to be rather dusty so I can only assume it is from the underside of the Hummer. 
 
My wife keeps the garage Operation Room clean, so I know it was not there when I left for the rotation & her Jeep has not moved since Thursday. 
 
Any ideas??    

This sounds like a plasic plug.  Open the rear door and look under the back end.  See if you see an oval hole.

I hear as you get OLDER, Things start to FALL OFF???

so.........what your saying,is you dont have much left

Check out this thread
 
http://www.hummerforums.com/m_22763/tm.htm

Nothin fell off here!! I checked ,..........twice.  Forgot I checked the first time.

 
Let us see it? Please.....?