^ I can't speak for the pounding, but as for the stamping. I'd be interested to hear if there is a pattern to it. If these people are doing these things at ungodly hours, it seems strange that they would be losing sleep regularly just to harass you.

Certainly if there is a pattern, then perhaps it is some activity or another they are doing.

I mean, how loud is it? Is it like loud footsteps, or is it like jumping up and down? Is the sound in one place, or does it move around? And as you said, is at the same times of day for similar lengths of time?

I totally believe you that it's happening, but I still see there being a rational explanation.

PS - I thought you said the person upstairs had a toddler or something. I seem to vaguely remember you saying you could hear them stamping around a couple of months ago or something. I'm sure you said that.