In my basement, where the water and propane gas pipes enter, I hear a noise periodically throughout the day which I can best describe as being like a light ball dropped on a hard surface from a few inches above, and then quickly bouncing a few times. I have visually inspected the area while the noise is occurring but can't locate the source (it may be coming from elsewhere and traveling along the pipes). It is annoying, as this is a finished basement and I can hear it in the living area.

Does anyone know what type of device might be causing this, where it would likely be located, and what it looks like?

We're on city water and sewerage, with a propane gas tank. I do see a couple of devices that look like regulators for water or gas pressure, but am not positive what they are (I just moved into Asheville, NC and am not familiar with things up here yet).

The sound does not seem to happen when water or gas or the HVAC system is turned on. It happens of its own accord. It might occur for a few minutes, then stop, then start up again later... almost as if a bit of pressure were being released, and there is some sort of a check ball at the top of a vent which lets the pressure out, but nothing in, and bounces a few times in the process.

Thanks in advance for any suggestions.

The first thin I would suspect would be the toilets. Let's reverse the washer first. Shut the water off under the tank and take the lid off. Remove the three screws on top of the ballcock,(sae image) and pull the stem,washer and float assembly up. Pry the washer out and turn it over. Seat it back firmly and see if that doesn't help.
Sometimes 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 noise. If not click on back and we'll explore farther. Good luck, Tom

Tom, thanks for your detailed response. I will give this a try when time permits and let you know what I find.

I assume I can test the theory by shutting off the water valves at all 3 toilets in the house (to see if it stops the noise) rather than having to disassemble the check valves in each?

If I'm mistaken about this, I hope you will let me know.

Thanks again, Tom -
Stuart

Ahh! You want the easy fix where you don't have to open up the ballcock and reverse the washer. The valve that would affect it most would be the valve under the tank. Let me know if it works. Tom