I heard them late at night while walking on the W&OD near Sterling Park and Ashburn earlier this month. Wouldn't be surprised if the explosions were because of what the above poster mentioned.
Earlier in the night a fucking Washington Flyer taxi was driving on the bike path too. Wouldn't be surprised if a bunch of spooks left from the tunnel with the taxi as a cover. Who knows.
http://projectcamelot.org/underground_bases.html