Weird consistent pipe knocking noise even when everything is off and valves closed

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I recently moved into a high rise building condo(36 floors) and within the first night I noticed a consistent knocking noise in the wall that is more frequent during early mornings and late nights, it is very noticeable and can be heard anywhere in the entire unit, it is driving my wife and I crazy and we would wake up at 3-4am in the morning because of it. We can't go to sleep without ear plugs now.

My building has a central boiler in the top floor and sends hot water to each floor/unit, the hot waster runs through the fan coil unit in each unit zone and output hot air. It flows in the following direction: Central Boiler-->Building Zone Main pipe that goes through floors(wrapped with rubber insulation) -->flow control ball valve of my unit(it is right by the building main pipe)--> zone valve actuator -->fan coil unit. No hidden pipe is unaccounted for here.

I opened up my air handling unit/fan coil unit cover and learned that the noise came from the hot supply valve and pipe going to the fan coil unit and I can feel the vibration in the pipe when the sound goes off . We have a four pipe system with 1 hot supply line/1 hot return line and 1 cold supply line /1 cold return line, the only pipe that vibrates when the sound goes off is the hot supply line, nothing on the other three. I asked my property manager and building engineer if my neighbors had the same complaint and apparently nothing had been reported, and if there is air in the pipes, everyone would hear it. This rules out the Building zone main pipe from the problem.

Please see the video I uploaded on Youtube documenting the sound:

I tried to troubleshoot on what might be the cause:

1. Turned off Nest Thermostat, noise persists
2. Turned off fan coil unit, noise persists
3. Turned off all the power in the entire unit (switched off breaker box main), noise persists
4. Manually closed the flow control ball valve of hot supply line, noise persists
5. Manually closed the flow control ball valve of all the pipes, noise persists

As mentioned before, the vibration can only be felt on the hot supply line as the sound goes off, this leads me to believe it might be the ball valve (valve that controls flow of water from building main pipe to our unit's fan coil unit) failing that's causing this noise because the noise kept going even after powering off everything and regardless of opening/closing the valve.

I hired a HVAC technician to take a look and he checked over everything including the zone valve actuator to make sure it was opening/closing as intended and it was. He arrived the same conclusion as me: faulty ball valve because nothing else seems to be the culprit, but before deciding to change the valve I wanted to make sure this is indeed the issue because changing the valve requires draining the pipe of the entire building, that's a lot of water we are talking about and we'd have an entire building without heat for a couple hours.

Thanks for the help!


Currently under Chemo Treatment.
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Orlando, Florida
The pipes are expanding and contracting as heated water flows. The home I grew up in had a hot water heat and in the middle of the night I knew the heat was on when the pipes started making noise. It was worse in homes with steam heat and cast iron radiators. I'm sure the previous tenant complained about it to the building maintenance but you can also try. It's not something that just starts but it might not be possible to locate the source in a big building. It could be a few floor away since copper (metal pipe) transmits noise quite easily. If there is a shared wall where you hear the noise, other tenant may also hear it.
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