OMG I used to hear it all the time whenever I'm at my bf's place. It was only yesterday that i found out it's not an independent case!

For those who have never heard it before, stand up, drop a marble on the floor (preferably marble flooring)-- that's the exact sound you hear, loud and clear coming from above you!!
Whenever I ask my bf what is that sound, he always tells me it's the kids above playing! This happens around evening time. And I'd get irritated coz' the damn kid sure makes a helluva noise! Anyway, when I found these threads and showed him, he told me actually his mom found out there are no kids staying in the flat above him!!
Why no one go and ask HDB?