It is the sound of people offering prayers outside Bangkok's Siriraj Hospital, where King Bhumibol Adulyadej is being treated.
They were wearing pink, a colour considered auspicious for the King.
There has been speculation about King Bhumipol's ailing health for sometime, and he has not been seen in public since January.
And this time, the usual upbeat medical report from the palace emphasising the King's recovery has been absent, leading many to fear he is close to death.
But Bangkok resident Jintana Makduangtien, among around 300 people praying outside the hospital, says people remain hopeful for his recovery.
"I believe that His Majesty is still fine, and I want everyone to know that he is well."
Another resident, Somchai Poopharkhan, says, even as he struggles with his health, the King remains revered by many.
"Even today, where he is unwell, we will always see him as a hard working king."
Anxiety over the King's health and eventual succession has formed the backdrop for more than a decade of bitter political divide in Thailand.
That divide has included two military coups and violent street demonstrations.
King Bhumibol, largely seen as a critical unifying force in the country, was born in the United States, in 1927.
His father died when he was just two years old, and, when his childless uncle abdicated in 1935, his nine-year-old brother took the throne.
But King Ananda was shot dead in his bed in 1946, so King Bhumibol ascended to the throne at the tender age of 18.
He has now reigned for 70 years, so most Thais today have not known life under any other king.
Bangkok resident Donnapha Kladbupha says the King remains an important symbol to many.
"The King is the heart of our country. So, without a heart, we cannot survive. So we pray for our heart, for the heart of our land. So … just only one thing, to make the King's health better. I want to see him to come and say hello to Thai people again."
The date of King Bhumibol's coronation is celebrated on May the 5th each year as a public holiday in Thailand.
Prime Minister Prayuth Chan-ocha, also head of the ruling junta, has cancelled an official engagement in the country's east and returned to Bangkok.
And Thailand's military government has released a statement urging the public to rely on official announcements about the King's health, not on social media.
