''odd structure''..I doubt it
The steel frame construction of this building is a pretty standard construction technique as far as I know. The steel columns which are concealed by the squared-off corners in the corners of most of your exterior rooms create problems for FM radio reception and tend to transmit noises between floors. I suspect that the only reason you notice it in the middle of the night is the absence of other environmental noise associated with diurnal activity in your unit. I usually hear the noise of washing machines which is why I refrain from using mine after a reasonable hour in the evening.
I can imagine that this information is not that informative, but I'm glad to see someone out here using the message board. You could probably get a better answer from Guy Zebert (an architect who lives in the building), Doyle Harp (an engineer who lives at HPT) or Dick Jones (a part-time resident, former HOA board member, and employee of the company that built the building). All three are active participants at monthly Board meetings.