Same thing happened while I was living in X condo (Great Gulf Developments). There was barely any soundproofing between the window wall and the concrete support beam, and so often times I would hear my neighbours having sex or simple things such as being able to hear your neighbour sneezing while you are laying in your bed. I could only imagine what they heard while me and the wife were having a hanky panky moment
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This shows you what I am talking about. The red arrows show the concrete support structure. Between that structure and the window wall is drywall, but it seems to lack any soundproofing. So say your living area is between those red arrows and just left of one of those red arrows is the neighbours bedroom (kind of how X and X2 are laid out), chances are you will hear everything that is happening in that bedroom.
The time when I heard my neighbours having sex, I was sitting on my sofa watching TV. I started hearing moans, so I "followed" the sound and it took me to that area which I highlighted. It was not a "deal breaker" for me, as I enjoyed the condo - however it was an interesting experience.