Periodic "thunk' from roughly behind shower head, but no relation to use of shower
Context: I live in a seven-story building with about 60-70 units total. I'm on the second floor.
For about a week, I've heard periodic "thunks" from roughly behind my shower head. They have a fairly forceful sound, kind of like the "water hammer" effect. But whatever triggers them seems to have no connection to anything I turn on or off.
It's almost always a single thunk.
They get into a rough rhythm of happening once every few minutes. This doesn't seem to match what someone in another unit using the bathroom would be like.
They can happen when I haven't even used the bathroom for hours.
If I happen to be showering when it happens, I can see the water get somewhat weaker for a fraction of a second.
I tried to get my super's help, but I couldn't demonstrate it for him. I read about sediment in the water heater having an effect, but he said that our building just isn't set up that way. He asked if it might be the heating pipe, but I know where the sound is coming from and its quality, and it isn't that.
Thank you in advance for any ideas as to what this might be.
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