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Thumping sound from water pipes

emaxxman00's picture

My water pipe is making a slight thumping sound. It's sort of like someone is very, very lightly tapping the pipe with a rubber mallet. It's very strange because I can't seem to locate exactly where the thump is.

- I have the hot/cold lines branch off at a T in the basement.
- The hot line does NOT have a shutoff except at the water heater and at the fixtures.
- Both lines travel ~15 ft to the left(kitchen) and ~8ft to the right before going vertical to the upstairs full bath.
- The 8ft run to the right includes a branch for the washer and a hose spigot outside (shutoff on spigot is in "off" position)

- At the T-intersection on the cold line, there are two ball valve shutoffs on each side of the T. (I had a leak on the joint late fall/early winter and took the chance to repair and add the shutoff valves.)

Is it the valves being so close to each other? I can't say for sure but it may have started after I put the valves in.

If not the valves, any idea what could be causing the thump? I can't actually hear it in the basement (where all of the pipes are exposed) so I suspect it's in the vertical run.

Is there air possibly stuck in the pipe? If yes, how do I get rid of it?

The thump occurs usually when there is no water running but I also hear it sometimes when the water is running.

There is no water hammer or pipe banging when I turn the water on or off.

I'm stumped.

(post #86066, reply #1 of 4)

If you something loose in the flow of water it can move around as water flows. And that moving can block the water and release and keep repeating.

And that can vary from any thing to a slow bang....bang....bang to a machine gun sound, to high pitched whistle.

Most often it is caused by a loose washer in a faucet.

But sometimes it is something loose in the line and when you did the repairs something could have gotten in. And even solder if you applies too much and it dripped inside the pipe.

But it requires water flowing. And then only water flowing through the valve or section of pipe with the problem.

And in most cases you don't have continous water flowing. One place is a toliet fill valve along with a leaky flapper. The valves themself often cause this, but it is a squeal right at the toilet.

Another place where water might be running continously is for an automatic humidifier.

A pressure reducing valve can also cause it and it for be for any more used in the whole house. But again water has to flow for it to make the nose.

In an other forum someone had a similar problem. And check every place and could not relate it to anything.

Finally found out that the city have pressure reducing valve in the main outside his house and it served a number of houses. And that valve was defective.

William the Geezer, the sequel to Billy the Kid - Shoe
. William the Geezer, the sequel to Billy the Kid - Shoe

(post #86066, reply #2 of 4)

Sounds that occur when no water is running are generally due to thermal expansion/contraction of the pipes. The pipe runs through a joist or some such and sticks a little vs sliding smoothly. As the length of the pipe changes due to heating/cooling the pipe will move in little jerks, kind of like how an earthquake occurs. Generally this will produce a sort of ticking sound, but it varies depending on how much the pipe sticks. If you can find the place where the sticking occurs there are plastic bushings you can install to make the pipe slide easier.

Another thing that can happen is that water pressure changes from outside the house can produce pipe noise. This might occur if there's a commercial building nearby that turns the water on and off fairly suddenly for some reason (perhaps just a commercial tankless toilet). This will be more like the familiar water-hammer thump.

Occasionally these sorts of sounds are amplified because the pipe is barely touching a heating duct or some such and vibrations in the pipes are transferred to the duct. Something to look for.

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(post #86066, reply #3 of 4)

Maybe somebody flushed a rabbit down the toliet!!!


(post #86066, reply #4 of 4)

Maybe somebody flushed a rabbit down the toliet!!!

that's kwazy!

"...craftsmanship is first & foremost an expression of the human spirit." - P. Korn