It starts with two young female voices, quietly at first, almost gently piercing the quiet of the night.
"Allahu akbar!" they cry out a few minutes after 10 p.m. "God is great!"
Then another voice joins in from the other side of the block. This one belongs to an older woman. "God is great!" she responds in a rasp that suggests decades of hardship and swallowed rage. "Allahu akbar!"
After a minute or two, a male voice joins in. It's as if he needed a little time to put on his slippers and clamber to the rooftop.
"Allaaaaahu akbar," he moans.
Within a few minutes a choir of voices erupts.
"Ya, Hossein!" a man with a sturdy baritone announces across the lush trees. "O Hossein!"
"Mir-Hossein!" a group of women shrieks back, every ounce of energy straining through petite voices.
"Marg bar dictator!" a voice erupts. "Death to the dictator!" And then more voices, a cacophony of anonymous anger. "Marg bar dictator. Marg bar dictator."
I have never thought of the quiet, leafy neighborhood where I stay when I'm in Tehran as particularly political. During the daytime, the only sounds are of water streaming through the canal.
My greatest concern has been to skip out of the way of the young guy speeding down the narrow street in his SUV, pop music blaring out his windows.
Until now, the most momentous events have been the rollicking parties some of the neighbors have thrown, which filled the street with cars of merrymakers.
But my opinion started to change after Iran's June 12 presidential election. Supporters of losing candidate Mir-Hossein Mousavi called for Iranians who had voted for him to climb to their rooftops between 9 and 11 p.m. and shout "God is great!" to voice their discontent over alleged vote-rigging.
The gesture harks back 30 years to the months before the Islamic Revolution. It was a way to reassure others that they weren't alone in feeling wronged and enraged.
Today it motivates people to attend the peaceful marches that have become the largest acts of civil disobedience in three decades.
On Friday, supreme leader Ayatollah Ali Khamenei, Iran's highest spiritual and political authority, laid down the law: There would be no reconsideration of the vote count. President Mahmoud Ahmadinejad's reelection would stand. No amount of pressure, even the hundreds of thousands marching through the streets, would make him bend. Protesters would continue at their own risk.
As Friday night approaches, I wonder whether Khamenei's prayer sermon will quell the voices.
When 10 p.m. arrives, there is nary a sound except for the wind brushing against the drapes. But then the silhouettes begin to emerge, lithe teens and potbellied men.
"Allahu akbar!" the two young women cry out across the rooftops.
Another voice joins in, and then another, and then another, building to a crescendo.
"Allaaaaahu akbar!" a deep male voice crests.
The voice is beautiful, and easily recognizable as the muezzin from the local mosque.
"Allaaaaahu akbar!" his rich voice echoes through the neighborhood. "Allaaaaahu akbar!"