I live on the 2nd floor of an 11 floor condo. Lately I have heard a loud gushing water sound under my kitchen sink when a neighbour runs their water. This occurs every time the neighbour turns on their tap. When I touch the hot and cold pipes under my sink, I can feel the water running through them. I do not feel any vibration in my kitchen faucet stem or handle. I do feel vibration along the wall beside the sink which is where the water stack is located (all the way up/down the wall). The building Superintendent and a Plumber could not recreate the issue when they visited the upstairs suite to investigate. Has anyone encountered this type of issue and, if so, any advice? Is it possible that this could be caused by the suite downstairs? Thanks!
Assuming you're just hearing it & not noticing any other effects from it. An other effect would be your sink trap's water or your toilet's water being sucked right out, which doesn't appear to be happening.
Then, I'm inclined to think the wall or pipe changed. What could have changed in the wall is that thermal &/or sound insulation may have shifted or completely fallen away. A pipe change would be the pipe shifting or settling down onto a structural member of the wall which could be just a millimeter of change. Now, having an avenue to transfer its normal operations.
Neither of these are catastrophic nor indicative of the pipe rotting away to a much thinner pipe. But, there may have also been work done elsewhere that brought the onset. It's more likely that it's just natural settlement issues from heavy trucks driving by, earthquakes, freeze-thaw, or normal pipe vibration.
Of course, it should be investigated fully & abated for your continued enjoyment. A building of that size should have access within the wall from the basement. I'm sure no-one will be happy about the journey, but 2nd floor is about as good as it gets.