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As @barclayscenter notes above, New York's Mass Transit Authority helped the Islanders create that horrid noise. Basically, it's a subway horn. This is a curious choice, because no one likes the MTA and no one likes the sound of a subway horn, whereas a lot of people liked the Islanders' old foghorn, both old and recent:
The Islanders seem to be following the Nets' footsteps in hyper focus-grouping the life out of their surroundings in pursuit of an #authentic #Brooklyn #brand, with equally grating results.