Re: Slab Leak
First thing you might try .....
Look at the water meter to locate the flow indicator to see if it's showing water flowing without anything open.
A mechanical meter there will be some sort of spinning pointer .... possible star or triangular shape.
On an electronic digital meter there will be a section of digits indicating of flow.
If your unsure what to look for ....... turn on a faucet to see the flow indicator on the meter.
Once you have found the flow indicator and if it does show a flow without anything running....turn off the angle stop valve to the toilets and check the flow indicator to see if it stops.
There are occasions where the fill valve in the toilet tank are the culprit.
If the toilets aren't the issue .... try turning off the main water shut off to see if the noise stops.
"" an ounce of perception -- a pound of obscure "