whistle in water line

I have just noticed that my main line whistles when water is run in the house. Didn't before.
The sound seems to be coming from the plastic pipe inside the wall after it passes thru the main shut off. It is loudest from under the house where it comes out the floor and not around the shutoff - which is mounted inside a closet on copper pipe.
There is no leak.
What is causing this???????
cher
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i'd suspect a partial obstruction since you say this hasn't always happened.
are you sure the main valve is fully open?
it's possible that a piece of junk got into the line. backflushing might be worth a try.
volume and pressure still acceptable?
house may be haunted?
good luck.
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wrote:

The pressure has always seemed low EXCEPT just when I turn it on. Not unacceptable. I think I measured 40 PSI at the outside faucet with nothing else running. There is a pressure regulator on it.
What should the pressure be with plastic pipe?
Is it normal for the pressure to drop a second or two after you turn a faucet on?
It takes a while to build up again so I notice it.

<<<<<<<<<<<<that's it!!!!!!!!!!!!!!!

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Not really. Replace your regulator.
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Cher, Your pressure reducing valve is kaput. Try turning the screw on the top of the cone shaped peace and see if the noise changes. If so it is the valve. You might try cleaning it but most likely it will need replacing. Pressure should be 45 to 65PSI. You should also not see a drop in flow after turning it on.
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Could an obstruction in the line give the same indication as a bad pres reg?
The noise really sounds like it is coming from the line in the wall before the reg, not the regulator itself - though the reg is close to the noise.
On Sat, 27 Sep 2003 00:13:51 GMT, "Dale Wilcox"

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it could but a faulty PRV is lots more likely cause of trouble.
i don't think you mentioned having a PRV in the original post.
for that matter, i would consider devices like reducing valves to be "obstructions" by their very nature.
some reducing valves are fitted with a strainer on the inlet to prevent small pieces of debris from damaging the valve itself. this would be a good thing to check first if it exists. look for a Y strainer before the valve or perhaps an integral basket strainer right on the PRV.
that very short period of adequate pressure as you open a faucet is probably due to pressure release of one or more air chambers in your system.
hope this helps.

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Actually, if there is an obstruction, the initial higher pressure makes sense. the water in the lines is pressurized when it isn't running. As soon as I turn it on, the water rushes out, then flows at the rate allowed by the obstruction.
It has always acted this way, but this is the first time I have heard it whistling. The whistling is definitely coming from a point before the PRV. Unfortunately, it appears to be in the wall. Maybe I can disconnect the PRV and run something up the line instead of trying to replace the pipe (behind the sheetrock job).
thanks for your help
wrote:

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Have you tried taking the main water valve apart to see if the problem is there? Sometime a split washer can cause a noise like that.

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Good thought. I'll look

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