Hmmmm, possibly but it doesn't sound like clasic water hammer to me (that's usually a sharp metallic bang, not a wooden thud). Your sounds more like a door closing (?) Do you have check valves in your water system?

@sktn77a -- i think it does sound more metallic bang-y in person :) It's definitely not a door closing. I'm not sure about the check valves - how would I find that out?

@Mr. Memes -- I wish it was! I can distinctly hear it coming from behind the walls as the water is running from the above units.

@klem1 why do you think that?

"One or more toilets are leaking in the building."

Good thought.

That sounds very much like what I have going on in my house. Mine, being single family, allows me to do more sleuthing than you can. For instance, I know that this only happens when the hot water is on and the pipes are hot (not when the hot water has not yet heated up the pipe). I also know that when the wall was open to remodel the bathroom, my builder put clamps to hold my pipes in place and it helped, but I still do have the sound and it is not coming from where we know the hot water lines to be! So, once the construction in the one bedroom is done, we are opening up that wall in the bathroom from the backside and turning on the hot water and figuring it out for good!

I will try to save this thread, and come back to it in a few weeks when the work is done. My builder had to go away for a family death, but will be back in a week or so, so don't expect to hear from me sooner than about three weeks or more.

It's most likely toilet(s) leaking because you hear the water running, but everyone says they're not using the water at that time. Or else they're lying, which is totally possible. How are the units heated? If they're heated with individual furnaces, a humidifier could be plumbed directly to one or more furnaces, which would cause you to hear water running and then draining. If heated by boiler, then the noise could be from that. Some radiators (whether baseboard or not) create more noise than others. If you tore out a plaster wall during construction and replaced it with drywall, any noise within or behind the wall would sound louder to you.

When staying in my brother's basement, I could clearly hear water running in the PVC waste pipes. I wonder if this sound is somehow amplified or otherwise able to be heard from behind the drywall.

Honestly I'm way less concerned about the water running noise than I am about the banging. The banging is way more disruptive. Water just sounds like water going through pipes.

So Lindsay,have you asked your neighbors if their toilets are constantly running then shortly going off all hours of the day? I figured you could handle talking to the neighbors. Ripping out walls and digging for hidden valves as suggested by others I'm not as sure of.

Klem1, I've reread this thread 3 times and I still can't find a single suggestion to rip out walls or dig for anything. Did I miss something?

OP, you may be less concerned about the noise from the running water than the noise from the banging, but they are related. What goes in, must come out, as they say. Find out what's making the water drain out and you will be closer to finding out what's making it run in. Think outside the box, and be very specific with the symptoms. For instance, do you only hear it when water is draining? Do you only hear it when water is running? Is it worse when it's cold out?

As stated in the initial post, there's no correlation between the water running and the banging. They appear to be separate issues. There is also no correlation between when neighbors are using the bathrooms and when the banging occurs. The only consistency has been that the banging has occurred at about 5:30 AM very frequently.

I could imagine that an apartment or condo with a central hot water system might start revving up for the morning showers around 5:30 am. I wonder if you have a central hot water system, and if you do, if it has a circulating pump to circulate the hot water through the pipes. It might be that the water is very hot at that time making the pipes expand and then bang. My problem, which sounds the same as your sound sample, happens when hot water is running through the pipes.

Might you have nocturnal critters living in the walls?

SR

Lindsay, my contractor fixed my sound that is so much like yours, today. For me it turned out to be the drain pipe coming from my vanity in the bathroom. Mine banged just like your sound when hot water is run through my drain. It turns out that there was a small piece of wood attached to the framing that was very close to the plastic drain pipe in the wall. When hot water made the plastic expand, it would hit the wood, bounce back, then rebound against the wood, bounce back, and hit the wood again. And so on. It started out sounding like a "tick" noise, but got louder with each hit against the wood, until my pipe was banging against the wood. Jim just sawed off the wood piece that was too close to the pipe, and the sound is now gone entirely. Like yours, mine sounded like a loud "SNAP" sound, often with a smaller "tick" sound following it, before another "SNAP."

Are you certain that a neighbor next to you or above you is not using the water at 5:30 every morning? Do you hear their movements so loudly that you would know every time they ran water in their bathroom sink?

I know that our problems may have a different cause, but I just wanted you to know the solution to mine, in case it helps you figure out yours.

Does your building have a water softener system? They are usually set to regenerate at a certain time of day.

Would a water softener make this kind of sound (either functioning properly or malfunctioning)? There is a recording of it up at the top.

Lindsay: I listened to your sound clip and it sounds exactly like an exhaust vent flap opening and closing (actually hitting back down). I have that issue with our kitchen hood roof vent which probably needs its return spring tightened; I can hear it only when it blows a gale where we live. If yours or someones water heater or furnace comes on at 5:30am, it is most likely the exhaust vent flap transmitting the sound back down a vent pipe in the wall. The waterfall sound is most likely a drain pipe from the floor/s above.

Have someone get to the roof to fix the vent flap if that's the case.

Hi everyone!

@Nancy in Mich Glad you were able to figure it out!

So, I put a hole in the wall three years ago and It's been there every since 🤣 I FINALLY got around to getting a contractor in here to do the remodel and said we can NOT put the walls back up until we figure this out.

It was frustrating because - while I was able to catch the banging on video in the days and the MORNING leading up - I was not able to replicate the noise live to them.

We definitely now think it has to do with the hot water. I've tested it with my neighbors above and it seems to occur when they run their master sink or shower.

The contractor/plumber believe it has to do with their hot water valve...something about it being too tight and not letting enough air flow....kind of like when you pour out a gallon of milk and at first and crashes bank into itself...and only pours smoothly when its half full and air is flowing.

Does that make sense to anyone?

Have your plumber install water hammer arrestors on your supply lines please.

We had this same issue at our new lake house a couple years ago. We thought for sure the house was haunted lol. We installed water hammers and it didn't help. The plumber was stumped. It ended up being bad shut offs on the toilets. Don't know which one, but after he changed the shut offs on all three toilets, we never heard the noise again. I hope you figure it out soon. The sound is maddening!! Good luck!

"Have your plumber install water hammer arrestors on your supply lines please"

Well, it's still not clear if it is water hammer(?)