Dripping noise in flat below's shwr room when I use my shwr

[seller392]

I live in a 2 flatted property. I have the upper flat which is on 2 floors and has an attic bedroom with ensuite shower / toilet. When I have a shower or flush the ensuite toilet my downstairs neighbour hears a dripping noise coming from her ensuite shower. If I run water in my downstairs bathroom or flush it's toilet she doesn't hear any dripping.
There's an inspection hatch in my downstairs bathroom giving access to the plastic drain pipe and all looks normal as far as I can see. There's no sign of any water leakage.

Can anyone suggest what's causing the dripping noise?
Many thanks

 

[JohnD]

does she have a shower enclosure, where there is a hidden void between the enclosure and the wall?

Or a plumbing duct, boxed in?

Showers usually leak where the tiles are badly sealed to the tray, or from the waste.

 

[slapper]

More than likely expansion and contraction of the plastic pipework creaking on joists when getting hot, if no leaks found

 

[seller392]

We both have shower enclosures. There is no evidence of water leakage - just the sound of water dripping.

I'm guessing the waste pipe from my ensuite (3rd Floor) feeds into the waste pipe that descends all 3 floors, also taking water from my bathroom (2nd floor) and ending in my neighbour's bathroom (all in the same vertical line). My downstairs neighbour's ensuite is to the left of this pipe. What's confusing is that the dripping noise is only heard when I generate waste water in my ensuite (shower or toilet - so it's not leaking tiles). Flushing water in my bathroom (2nd floor) doesn't result in a dripping noise in my neighbour's ensuite.

Could there be a 2nd waste pipe connecting the ensuites?

 

[longdogs]

Just an idea but I have come across waste pipes pushed too far into the stack pipe resulting in water from above dripping on the protruding pipe.