There are gratings in the sidewalk all over Manhattan. Some blow warm, moist air up your trouser legs as you walk over them, others emit rumbling, grating sounds from the subway. You’re left with the impression that there is some kind of civilization down there, quite independent from our own.

I’ve always made rhythms out of the sounds I hear. A train journey can become a two-hour concert of recurring themes and unexpected interruptions to the pattern of clacking as the wheels pass over the small gaps in the track put there to allow for expansion of the metal lines in hot weather.

In Times Square, amongst the hurly-burly of the traffic we passed a grille emitting just such a regular, rhythmic rumble. It was reminiscent of a mechanized loom with its synchopated but constant cycle. In my mind I added some samba cowbells and the surdo and found a rather good fit. And in the time it took me to walk past the grill, the rhythm only varied in distinctly musical ways. I doubled back and stood a moment, listening intently to the ground beneath my feet. The New Yorkers studiously ignored me while Rachael wondered what was going on.

My first thought was that there was a tribe of gnomes in this underground world having a party. I figured this was unlikely even in New York. The next theory was that there was a samba band practising in the basement of the building next to us. Then with a flash of inspiration I realised there was probably a subway station here. Sure enough there were the telltale globes-on-pillars across the intersection. A swift New-Yorkian jaywalk saw us descending to the subway station where a guy with a bass drum and cowbell was accompanying two guys playing industrial-sized paint tubs. The sound was fantastic. I was forbidden from filming them but threw a few dollars in the hat when it came around.

When they finished it turned out they were selling CDs. Having just donated, I didn’t have enough cash to buy one and they seemed pretty hostile so I didn’t bother haggling too hard to spend the last of my cash on them.