Mr Goh, 37, said the marble sounds can be traced to air-con pipes or old refrigerators, while the sounds of furniture being
dragged across the ceiling, another common occurrence, could be due to lift doors opening and closing. Water hammer occurs when water flow is shut off suddenly like when the toilet is flushed. This change in pressure rattles
the piping and create 'clanging'sounds, which may sound like marbles dropping after distortion through concrete walls,
he said.
Three explanations
1) When water flow is shut off suddenly, the change in pressure rattles the pipes, which may sound like marbles dropping
after distortion through walls
2) Some pre-fabricated floors used in HDB flats have an embedded high-strength steel cable which can give off creaking
sounds when they contract.
3) It is really children playing with marbles
This should help, I think