You’re just about to go to bed, but you hear the sound of marbles bouncing coming from the unit above you.

The last time you checked, the neighbour upstairs doesn’t play with marbles. Or worse still, the unit upstairs is empty.

Urban legends suggest that it could be a “Toyol” at work. For those unfamiliar with the Malay ghost, it’s been said that the toyol takes the form of a small child and believed to have a weakness for marbles.

Fortunately, a post on Monday on the Punggol Waterway’s website - which seems to be created by residents living in the area - debunked the idea of the supernatural imp dropping marbles in the middle of the night.

Here are some possible reasons:

1. Change in pressure in toilet pipes

According to Answers.com, the sound could be created by the change in pressure in toilet pipes. This causes a vibration in the pipes and creates the sound of marbles dropping.

2. Water bubbles in sanitary pipes

A sudden change in water flow mixed with soapy bubbles will create air pockets that burst and echo through the pipes. The sound it creates is similar to that of marbles dropping. However, this usually produces a single sound.

3. Opening and closing of the mosquito trap mechanism

The sound of running water opening and closing the mosquito trap mechanism in toilets could sound like marbles dropping.

4. Water dripping during air-con condensation

Water dripping within pipes after air-conditioner condensation could also create sounds similar to that of marbles dropping.

Are you convinced by these reasons? Or do you still think that your HDB flat is haunted?