[quote=Hobie]I suspect your tile was not installed on a cement board base. Glue down hardwood upstairs is very common and will actually strengthen the floor by bonding the subfloor to ply to wood floor.[/quote]

You are probably right about the tile…I ended up firing the guy for other reasons, but I suspect he took shortcuts on the tile install too. Learned a lot of lessons by hiring that guy…

Thanks for the tip…I’ll file it away for when I go out for flooring bids next time.