Hot Water Drain Making Noise

no leaks. The drain pipes are made of black plastic.

feel a small amount of vibration.

I have a very similar issue, also in an upstairs bathroom, although I would describe the sound as rather loud clicks or bangs of one solid material against another, not dripping. I think in my case the issue is the 2-story-high straight drop of the drain pipe just before a 90 degree turn - the water drops 10-12' down in irregular splashes and then hits the bottom really hard making the pipe move a little and bang against a bracket (which I'm yet to identify) or a stud somewhere inside the wall.

I'd be honest, it never occurred to me to open the wall even though the phenomenon is really annoying (and can probably cause a leak at some point), so I'm just wildly guessing at this point. However, nothing of the sort happens in the lower level bathroom or another one upstairs that has drain pipes laid out differently.

If someone has a better idea about what could be happening to make those noises in drain pipes, I would love to hear that as well.

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