Residents across several Alabama counties experienced a loud boom on Tuesday, but no one seems to know what caused it.

Reports of a boom loud enough to shake windows in many houses were heard across St. Clair, Jefferson, Cullman and Walker counties during the day on Tuesday. Emergency officials received calls about the boom but have had no reports of anything the could have caused it. 

The U.S. Geological Survey said there was no sign of an earthquake. 

The National Weather Service posted to Twitter: “Re: loud boom heard: we do not see anything indicating large fire/smoke on radar or satellite; nothing on USGS indicating an earthquake. We don’t have an answer, and can only hypothesize with you. 1) sonic boom from aircraft; 2) meteorite w/ current Leonid shower?”