Toilet flush -*thump*..... doesn't seem to be water hammer

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Zebulon

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I recently moved into a 8 year old town home and have been experiencing an odd noise when flushing the 3rd floor master bath toilet. When the toilet flushes, about 1 or 2 seconds after the flapper closes there is a 'thump' in the floor below the master bath. It sounds almost like a door closing downstairs. When you're downstairs, it sounds just like someone closing the master bath door slightly hard.

The house had high pressure due to a broken pressure regulator. That had been replaced and the pressure is now around 50 PSI. It doesn't seem like a normal water hammer issue because the noise happens long before the fill valve in the toilet closes. It's almost like the flapper closing is causing the noise.

Any ideas what it could be? Is the weight of the water causing a pipe to just move in the floor on its way down?:confused:

Thanks.
 

Terry

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Many flappers will thump when they close? The American Standard Champion is one that comes to mind, but it could be most any other brand too.
 

Zebulon

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I tested the flapper theory by flushing the toilet but not lettting the flapper close. The 'thump' noise is still there, about a second or so after the water drains from the tank. It's seems to be coming from the floor about 5 feet away (i'm guessing where the drain pipe is). Is it possible that there's a venting problem causing this noise? Other than that, I'm wondering if the drain pipe is so loose it's flopping around inside the floor joists.
 

Jadnashua

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Sounds like it may be the drain pipe moving, probably from where it makes a turn and it hits something. If you could reach it, a clamp or some padding might stop it. Note, some flush valves open quickly, and can make the pipe move, too. Try turning off the water supply, flushing the toilet, and see if it still makes a thump. It might be a sticky valve or a pipe.
 
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