Downstairs neighbour says floorboards are vibrating

My suggestion would be to work with your neighbour to determine what it is you are doing/where you are walking when the vibration occurs. Get someone to move around in your flat whist you listen with your neighbour in theirs (assuming they will agree to this). In my experience it will more likely be a joist or joists that are maybe not sitting properly and this is causing the whole floor to bounce and resulting in the vibrations described. Another possibility is that pipework has been fitted by chopping in to the joists and resting the pipes in the grooves created but not actually secured in place - as you walk on the floor the boards then cause the pipes to bounce and vibrate. By carrying out the check as suggested you can have a good idea what the problem is which you can then post on MyBuilder as a job. You should then at least get confirmation of the problem and an idea of cost to resolve. If reparation work is needed carpets will have to be pulled back or possibly taken up but they can be refitted. if it is the pipes as suggested this could be a relatively quick fix to just secure them to stop the vibration. If it is the joists that need securing this may be a slightly bigger job but neither are huge.

I would agree with what sand man is suggesting for this problem.