That's the sound a CTA bus makes, roughly 75 times each way, heading up and down Diversey Avenue between Harlem and Sheridan, its engine struggling to push ahead even though everything else - traffic, automotive operating mechanics, ridiculous racial and socioeconomic divides - tells it to just stop moving and quit now while you're ahead.
You hear it pulling out of the Logan Square Blue Line station when that old woman dares have a walker and (gasp!) keep the whole bus waiting an extra 30 seconds while she maneuvered on board and eked her way past her fellow riders too engrossed in their trips and too enraged with this woman's situation to give up their seat for her.
When the guy gets on at Western and starts throwing a fit because the bus driver won't make change for a five, the engine groans again as the driver, not knowing what else to do, tells the guy to either shut up or get the hell off and pulls away.
It's the sound it makes around Damen as the glimpse of Hell that is the Lathrop Homes rises up along the river, gaping holes where there were once front doors and steam rising up through the sewer grates. Past the playing field that sits abandoned, past the broken and boarded-up windows of apartments that people are still living in, past the open secret that soon enough, these places will be torn down and everyone inside will have no place to go.
You hear it when the girl who doesn't know how the CTA works gets on at Paulina, tells the driver she needs to get to some intersection considerably north of Sheffield and Diversey, then gets upset to hear there's no Sheffield bus.
"Don't you know how many people live on Sheffield?" she asks.
"That's not how it works," the driver explains, unaware of just how true that statement is.
It's the sound at Clark Street of more transit options than anywhere else in the city running at full operation, day and night, helping rich and busy people do rich and busy things.
And when all is said and done and that hateful trip across town is over, you hear it again one last time as the beast pulls away from Sheridan Road, a mechanism working against itself in a city that operates despite itself.
But the day is young, you say, and the park sure looks nice. They should all be such postcard views.