Under slab water leak

My in-laws are hearing running water when inside their shower. I turned off the main and bled the lines and it stops. When the main is back on, the sound is back. So I'm sure it is a water leak either in the wall or under the slab. Unfortunately, both sides of the wall where the sound is coming from are tiled. If I remove the shower faucet, that will give me a small access to the inside of the wall, but it is too small to see very well. Is there any way I can probe down to determine if the leak is in the copper ging from the slab up?
What I want to do is make certain it is an under slab leak before I have someone come out and re plumb the entire house.
Thanks in advance.
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Most large plumbing firms have the electronic equipment to sniff out the leak. I had a slab leak when I lived in Florida. One plumber wanted to rip up a big section of tile and concrete to look for the leak. I called this other firm and althought the test is expensive, it costs a lot less that rip up and guess. They pinpoint the leak at the edge of the laundry room and we just had to rip up two tiles and found the leak at the bend of copper pipe coming out of the slab. A lot cheaper than replumbing the house.
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Leak was under shower stall and they wanted to bust up a man size hole next to shower and go down and over to fix leak. Was able to seal off that line in adjacent bathroom through wall and then come up over through attic to bypass leak. Unfortunately because the water leak was below the slab, the insurance company took the stance that since no water came into house, there was no damage covered by insurance. So the whole $3000 bill was my liability. And then over the next couple of years, the "expansive soil" that was soaked swelled up and cracks developed all over the house...still not covered by the insurance as they "don't cover settling, even if caused by something covered by insurance". Oh well, a lot of patching covered the cracks and I sold the house and moved back to Illinois. By the way, a person with a little larceny in his soul would have poured some water on the floor under a cabinet or in the closet and then the insurance company would have covered some of the repairs. A couple of years after the first leak, another developed near the kitchen outer wall and water came up along the edge of the slab and under the cabinets and most of that was covered by the insurance company.
Tom G.
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On Mar 5, 6:50 am, snipped-for-privacy@gate.net wrote:

First of all do they have a hot water re-circ loop? Maybe there is no leak, just the hot water loop making noise.
You might be able to locate the leak by using the hot water......
I was at a friend's house & they said "there's a warm spot in the family room floor".
The floor had a warm spot about 12" in diameter. I told them unless they had hot water loop that they had a leak in the hot water pipe running from the WH to the kitchen.....sure enough when the plumber (I have more than enough projects at home to keep me busy) broke through the tiled floor & slab he found a leak in the hot water supply line.
Check to see if the noise goes away when you shut off only the hot water. If not, then you have a cold water leak.
Here's where it gets a little tricky, if you feel comfortable doing this....plumb the hot water into the cold water serving the bathroom, crank up the water heater temp a little. Turn the water back on, the leaking hot water will warm up the wall or floor in the vicinity of the leak.
Your other alternative is to hire a leak finding service.
cheers Bob
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Great advice. I like the idea of plumbing the hot water into the cold supply and feeling for a hot spot. However, I'll just recommend they get a company that has a tester.
My BIL had to have his entire house redone through the attic and it was quite an extensive job.
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On Mar 5, 11:03�am, snipped-for-privacy@gate.net wrote:

PEX helps a lot to replumb a home today
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Are you sure they are not hearing things. With all water usage stopped, does the water meter show any usage. I would start there, and then go to the other suggestions posted.
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On Mar 5, 8:50am, snipped-for-privacy@gate.net wrote:

Sound goes through pipes in the shower its magnified, look at your toilets first maybe one flapper is bad, you can put dye in the tank and see if it goes in the bowl. You can buy a moisture meter cheap that will find a wet spot in concrete if its not the toilet
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UPDATE!
I did determine that they have a sizable leak even when nothing else was on - turned off the toilets and water line to ice maker, etc. You could watch the small indicator on the meter turn. I als realized the shower is right where the main water line enters the house, so that is why it is heard there.
My In-laws called a plumber and told them they suspected a leak under the slab, in a wall, or from the meter to the house, since I'd ruled out any obvious other leaks from fixtures. They came out and spent 1.5 hrs verifying what I had confirmed, but they did not have a device to detect leaks under the slab and suggested my in-laws get a company that could do that. They paid them for the visit, but I would not have been so nice since they told them it was probably a leak under the slab or in a wall.
So another company comes out and I suppose used an acoustic type detector (I was not there) to find the leak under the slab between the kitchen and where the line enters the home. My next job was to dig up the line from the meter to the house and hope the leak was there, but this pretty much confirms it is really under the slab.
A few years back I had a small leak in a copper line right in the wall, from pitting corrosion or something, and never realized how lucky I was that it was above ground.
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UPDATE 2
The leak is a cold water line leak and the plumber says they can just replace this one offending line by running PEX through the attic. I don't see any point in redoing the entire house in PEX right now. Any opinions?
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