I wandered down what looked like a tranquil pedestrian lane away from the Hereford shopping crowds. Mansion House Walk in Hereford near the town centre.
I heard this mesmerising nimbus roar from a commercial kitchen HVAC. That was the wide silvery tube in the header pic
Not something you want to live next to! Fortunately there don’t seem to be any houses or flats nearby.
XY recording, Olympus LS14