First see if you can get to the back side of the tub from the wall on the other side, some places have a panel were you can see the back under the tub at the faucet end. If not your going to need a plumber for this one. Sounds like you have a leak at your wast and over flow, but at the wast part. under the tub.
Don't Call the plumber yet! Find out more at www.coolplumbingvideos.com
Don't Call the plumber yet! Find out more at www.coolplumbingvideos.com