It's probably the sound of traffic, thought Mr Gan Hwee Sun, 72.
He continued with his shower around 8am on Friday. Then one of his flatmates shouted in Hokkien: "Fire, fire!"
Mr Choon Siew Weng, 56, yelled that fire was raging near the front door of their one-room unit in Block 115, Ang Mo Kio Avenue 4.
They had to get out through the kitchen window of their second-storey unit.
He ran to the kitchen, climbed out of the window on to a ledge and jumped down.
The others in the flat, Madam Teo Siew Choo, 50, and her brother, known only as Mr Teo, 37, also ran into the kitchen.
Mr Teo then followed Mr Choon in jumping out from the ledge.
Madam Teo and Mr Gan climbed out of the window but didn't dare make the leap. They stayed perched on the ledge while clinging to their kitchen window. They were later helped down by cleaners.
Madam Teo was later taken to Khoo Teck Puat Hospital (KTPH) along with her brother, Mr Choon, and an elderly neighbour who lived on the third storey.
Singapore Civil Defence Force firefighters put out the blaze within 10 minutes. Residents from the second to fifth storey of the block were evacuated as a precaution.
Most of them are elderly.
Mr Gan told reporters that he and Madam Teo were members of a Chinese band which plays at funerals.
At KTPH, Madam Teo recalled she was woken up by an explosion.