There are two sinks in the master bathroom. It does not matter which one I use, there will be this dripping noise.
I have removed the stoppers and disassembled all pipes from both sinks to the wall and could still hear the dripping from somewhere inside the pipe going down the wall.
I used a long bottle brush and tried to clean the inside drain of any possible debris.
No such luck. I put everything back together, but, just like before, the dripping noise starts a few minutes after using an upstairs sink. There is no leak anywhere, just this noise driving me bananas.