I would like to know how to fix a water leak that is inside the wall between two bathrooms.
I can here the sound of water but water meter is not or is moving very slowly.

Have you found any water anywhere on the floors near the wall where you hear the sound of water running? If you have not found any it is possible that the leak could be under the floor, and if you have a concrete slab it could even be under the slab.

A pin hole leak under pressure sounds like a hiss. If you have a in wall leak you should see moisture around the baseboards. Perhaps it's not a leak if the meter isn't turning. Knocking, popping, creaking and crackling pipes are a common complaint, especially in colder weather. I can tell you what's happening and take the mystery out of it but you're not going to like the repair. When a draw is made on a hot water line the line expands against a pipe strap next to a stud and when you drain hot water from your tub or shower it goes into a chase that is a little cooler then room temperature. The heat expands the pipe causing it to rub against the stud to which it is pipe strapped. This is the sound you hear. As it cools it contracts and the noise is heard again. To repair it you must tear open the walls and locate the pipe strap that's causing the problem and shim it tight. Most people when they learn what causes it just elect to live with it. Regards, Tom