Noisy Neighbours and Marble Dropping

Okay, I have been doing some research and some thinking and I think I have solved one of the mysteries of HDB life; namely the neighbour dropping something like a ball late at night. It seems to be a wide-spread HDB phenomenon and is usually described as 'marbles'.

Some official comment blames water-hammer, but some independent commentators blame old aircons.

So after considering my situation I think it is the neighbours old aircon. It didn't happen for the month and a half before she moved in, and it doesn't explain the stamping and door slamming at 3am. But the 'ball dropping' would appear to be the old aircon 'relaxing' late at night, even though it is usually still turned on. With the cooling of the outside air at night the aircon has less work to do to get the same cooling effect, and as it makes adjustments accordingly the older ones can propagate pressure waves that flow back along the coolant pipes.

Apparently complaints about neighbours above dragging furniture across the floor can often be traced to the sound of lift doors travelling through the concrete. I don't know how that explains my neighbours dragging of furniture as it didn't happen before she moved in and it reduces in volume when I bash loudly on the wall.

And neither of these deals with her stamping loudly, continually opening and closing her (sliding) bathroom/toilet door, and slamming her bedroom doors. Nor does it explain the issue of the neighbour on the other side singing loudly at 2 or 3 in the morning.

But it does answer one question that was puzzling me, and that makes life a little easier.