PEX tubing sounds - running water or air in the line?

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Matt H

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There is a sound coming from inside the wall for my cold water line of my PEX plumbing line to bathroom sink A. It sounds like there is air in the line or maybe running water

Background
-2 story home with a PEX plumbing system with the PEX mainfold located on the 2nd story.
-The builder saved cost and did not install shut off valves underneath the master "His and Hers" bathroom sinks located on the 1st floor. Bathroom sink A & B.
-My home was flooded by a recent hurricane and so the water was shut off at the PEX manifold for several weeks when the bathroom had no sink. I installed installed new sinks and faucets for down stairs
-Bathroom sink A went from a 3 handle basic bathroom faucet to a vessel faucet with a single handle.
-Bathroom sink A had a leak on the hot water line, resulting in the hot water line being shut off and the cold water line open to the sink for a period of time.
-Now that I have fixed all the leaks and installed shark bite shut off valves under the sink, I'm ready to use that sink again. Unfortunately, when I have the cold water line open at the PEX manifold, the sound of what seems to be air in the line (or running water) is heard coming from inside the wall by the bathroom.

-There is no sound coming from the inside the wall for bathroom sink A's hot water line.
-There is no sound coming from the inside the wall for bathroom sink B's cold or hot water line.
-The sound continues whether the faucet is on
-The sound continues even if the newly installed shut off valve is set to "closed".
-The sound only stops when bathroom sink A's cold water line is turned off at the PEX manifold.

Suggestions?? Possible causes?

Thanks.
 

Reach4

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Possible causes?
When you turn the faucet to cold, and open the manifold valve, does water come out?

Check your water meter for an indicator that can identify low flows. Open that manifold valve, and see if there is water running. I suspect a pipe leak in that pipe. You could test for that in various ways. For example, maybe you could adapt the aerator to a fitting, and blow air. See if the air pressure holds.

Maybe block the aerator with some plug method. With cold manifold valve closed but faucet turned to warm, do you feel warm water in the cold pipe as it flows thru the faucet to the possible leak? Does the water meter show flow, even though it should not in that condition?

I am not a plumber.
 

Matt H

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When the manifold is set to open and the shut off valves are open on sink A, I can get both hot water and cold water. Pressure is normal. Water sputters for a few seconds and even sent water shooting out (thus belief for air in the line). Moved the faucet to "hot water" only, "cold water" only, and in the middle. It all works properly and good pressure.

So I doubt the sound is actually running water inside the wall.
 

Reach4

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With the faucet closed, and even the Sharkbite valves closed, you get a sound when the cold manifold valve is open. How would air or water cause a sound if there is no flow through a leak?

Do your pipes travel the distance thru the walls, or do they travel under or in the slab. I presume you have no crawl space or basement.
 

Matt H

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Reach4:
When I think about all 4 water lines going to sink A & B, and how I didn't do anything different with the cold water line to sink A, it doesn't make sense how I could have a leak.

If there was air in the line, from the manifold to the shut off, that air is trapped in the line and water would still try to move around and push the air out of the way? However, I understand the point of your question

The PEX pipe travel THRU the walls from the 2nd floor down to the 1st floor.

As of yet, I haven't seen anything indicating a water leak near that wall.
 

Matt H

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Reach4:

Going thru walls from the 2nd floor to the first floor, the PEX line won't travel through the slab. Plus when my walls were open (again flooded from hurricane) it was evident the lines were headed towards the 2nd story.

Just confirmed the wall adjacent to the sound is dry. I will perform the an air pressure test. That will definitely answer the question of a leak or not.
 

Jadnashua

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There won't be any air in the pex after a few moments...the water pressure will not bypass the air, it will push the air out of the line.

The new metal shutoff valves may be making some noise if they are not fully opened.
 
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