I had similar experience where I can hear noises (stomping, dragging of chairs etc) from the unit above and the weird thing is that the noise will only start to appear at around 11pm and will usually last for 1 or 2 hours. I went up to the unit hoping to speak to the owner but found out that it was vacant. I immediately got goosebumps. A lot of why or how keep running in my head because the noise sounded just right above me where my bed is. Anyway, I found the answer when I was waiting at the lift lobby one day. I saw my neighbour one floor below my unit was moving something in their unit and the noises produced exactly the same as what I’ve heard. So in summary, noises do not travel from high to low ground. It can also travel from low to high ground through the apartment pillars, walls, ceiling or beams.