That was actually my first thought. The city has been doing a LOT of sewer work in my area. Problem is, all of my neighbors know we have a clog, but none of them seem to have one as well. My wife looked it up online, and we can call our city sewer works and have them come out and check the city line to make sure it's not clogged where it meets our lateral. If it is, they will clean it out for free. If not, back to the drawing board.