I installed a new toilet in the 2nd floor master bath on October 2011. About 3 weeks ago (June 2012), I noticed a leak coming through the ceiling on the 1st floor directly under the toilet.

My first thought was to replace the wax ring, so I tried that and the leak persisted. The toilet is up against a wall, and the drain pipe runs about 8 feet and drops down the opposite wall. When I turn the water off under at the water line below the tank, the leak stops. This means it can't be a leak in the line right? Otherwise it would still be leaking unless I shut the main off?

At this point should I start thinking about ripping up the tile and sub-floor?

Thanks for any help!