Is it possible to hear a water leak in the walls but where the pipes come through the slab there is no sound?

if you cant find it in the house there is the chance it is in the slab or underneath if you can pressurize the pipe with air after draining them the leak will make a lot more noise. if you cant find it that way , try isolating different sections of the plumbing to narrow it down, Un fortunately if you need to ask how to find the leaks you should probably call a plumber!