I was fascinated by a birder’s observation that sparrows sing louder on the Rose Kennedy Greenway than in places in the countryside because they need to sing over the ambient noise in the big city.

Years earlier, I had heard the aggregation of ambient noises posited as one possible explanation for the Windsor Hum, the mysterious rumbling noise that caused sleep deprivation, earaches and nausea in the Canadian city outside Detroit. Later, the hum was ultimately attributed to blast furnaces at a US Steel plant.

It all got me wondering what are the components of ambient noise?

On the Greenway, it’s like Busytown. Sirens from emergency crews leaving Boston’s main fire station on Purchase Street. Trucks, buses and cars idling even years after the Central Artery gave way to the garden park. Low-riders and touring motorcycles are all about the bass. News helicopters. Planes arriving and departing Logan. Tower cranes. HVAC units. The sneaky, cocky sound of high-finance makes a hum of its own. When a meteor recently caused a sonic boom in the region, “a bunch of readers thought it was just another typical Boston sound,” according to a piece in the Boston Globe’s aspirationally hip vertical called the B-Side.

In a not-so-sleepy suburb, hear leaf blowers and other gas-powered lawn equipment. Delivery vans. Pop music on radios. Back-up alarms and the playing kids whose lives they save. Pickleball courts. Basketball dreams. Fathers recalling glory days as they teach their kids what to swing at. Wiffle balls pinging off wiffle bats. Generous women arguing about who picks up the tab. Even the chirping of other birds I suppose.