I live rather close to Miramar Marine Corps Air Station and sometimes, we hear a C-5 Galaxy (or was it the C-17 Globemaster?) rolling across the sky. That plane flies relatively low for awhile after take off (It flies pretty damn low all the way to the Pacific Ocean). It makes a ton of noise as well (sets off car alarms whenever it passes over).
Probably was a bunch of those huge cargo jets going over?