had almost the same problem and it was a hot water pipe that was seeping.
cost was about $1200 to dig up concrete slab and repair leak (repairing leak
was the easy part).
a good leak detector company can prove you right or wrong.
I have a strange thing going on that no one can seem to figure out. In my
house I have ceramic tile (underlying the tile is a cement slab) installed
several years ago. In a small area near the kitchen, about 2' by 2', the
tiles are noticeably warmer than the other tiles around them. That is, about
4 of the tiles are affected. They look no different than the other tiles.
They are not near any heat-producing appliances. It is not caused by the sun
hitting the area (the area is far from a window). There is no water leak (I
checked my meter, and it does not move unless I have water running from a
faucet). Any ideas? Thanks,