> To listen, go to bostonglobe.com/soundtrack. Rhythm is everywhere. In the heartbeats of our chest. In the language we speak. In the footsteps of our stride. In the bump-bump of cars over uneven asphalt. I remember a professor of mine recounting the day he got hip-hop; he’d been in Brooklyn, listening to the city pulse. Much of what fills our ears has a meter, whether we’re conscious of it or not. I think about this every time I get gas, for instance. The pumps at my local Shell station perform a consistent, reasonably complicated pattern in disgorging their fuel. I recently came upon another such cadence at Logan Airport. Returning from a trip, I went to collect my suitcase from the Terminal B baggage claim. As the belt on the carousel came to life, so did the beat: a series of clack-clacks keeping 4/4 time. Best I could tell, the pace was just above 50 beats a minute. Every once in a while the carousel would throw in a stray accent, but those, too, seemed to be in time. I don’t know what makes the moving rubber plates sound like they do. I just know it makes their pedestrian task a bit more interesting.