Our home is about 4 years old. A few weeks ago we started to hear a loud noise in our pipes (kind of like a prolonged groan). It started once every few days and grew to occur several times a day.

It usually happened after the shower was turned off, but occasionally when the dishwasher or washing machine was used. Sometimes it happens once, sometimes there are several small sounds ones after a big loud one.

We assumed it was water hammer. To attempt to fix the problem we followed some online advice and drained the water system at the lowest point. We don’t have a basement so we drained it at the plug at the water meter. The sound did not return immediately, but after about a day of regular water use it did return. We tried draining the system again with the same result.

The sound is loudest in one bathroom so we tried turning off different valves to see if there was an effect. As it turns out, when we turn off the fill valve of the toilet there is no sound. That toilet has been turned off for 4 days now there has been no sound whatsoever.

While we have apparently isolated the area of the problem, we have no idea of the exact cause or how to fix it. Should we replace the fill valve, the ballcock assembly, the flush valve? Or are we not even on the right track?

Thanks for any advice.

My bet's on the ballcock. It sounds like the problem is caused by the ballcock trying to fill while water is seeping out of the tank. The sound you hear is the washer vibrating against the seat of the ballcock. First check there linkage between the flapper and the flush lever. It should have 1/4" of play when your tank is filled. The water level should be 1/2" below the white overflow tube after the tank's filled. Next feel the flat side of your flapper. Does it have wavey edges? Do your hands come away black? Replace it if it does. And last check the seat itself. Any nicks or rough spots? If so click on back. There are replacement seats that glue right over the old one and are easy to replace. One of the above should take care of your howling. This happened in a new house some years ago. Only at night and in the early morning. They thought the house was haunted and were about to move out. I caught it in the powder room toilet. It would vibrate and the pipes in the wall would pick it up and carry it all over the house.
One more thing. This could also happen if the ballcock kicking on every time you shut off a faucet. To check this out remove the lid and open and shut the shower valve real fast while watching the float ball. If it bobs up and down you have located the source of the problem. It is a sort of water hammer and you don't recharge your air chambers by simply dramning the system. It's more complicated then that. Let me explain.Back in the 60's we were required to to put air chambers on all bath lavatories and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will began to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out TOM