brian...that could be condensation building up in the heater box and not draining out.
there should be a drain somehwere on the firewall to allow excess water to drain out of the heater box.
if it is clogged the water will backup in the car and drip in the floor.
had a customer at the garage last year with this problem.
she would come in every couple of weeks when the water starteddrippin on her feet.
i would put a hook made out of stiff wire into the drain and pull out insulation that mice had taken and started making nests with.
about 2 gallons of water would come rushing out tof the drain!
