two objects near O'Hare, July 2007

In the first week of July, 2007 I observed something interesting in the vicinity of O’Hare airport.  
I work in Oakbrook Terrace, IL in the only tall building around, Oakbrook Terrace Tower.  My office is on the 15th floor and faces NE. 
I was looking out the window at a more northerly angle, watching planes making their approach to O’Hare when I noticed a dark gray cloud, for the lack of a better word, hovering near the airport.  I say "cloud" because the edges did not seem well defined.  From my vantage point, I would estimate that the "cloud" was about a quarter to half mile south of the airport, at approximately 500 ft off the ground.  The "cloud" was  about 150-200 ft in length and 50 ft in height.  
I thought it was a strange cloud at first, but watched because it was so odd looking and just a little out of place.  There were high level clouds that day but nothing anywhere near as low.  After a minute, another identical cloud approached the first from the north and hovered at the same height about 100 feet away.  The first cloud then slowly moved off to the north, followed by the second cloud about 15 seconds later.
 I have kept an eye on that area since and have not seen anything else out of the ordinary.
 ------------ ]           ] ] ohare     ] ]           ] ------------  O objects     O  Oakbrook tower
Witness indicates that the date of the sighting is approximate.  PD