One thing Ian mentioned to me when I was having strange noise problems with my first 500, was that sometimes air can escape around the amp plate, driver, etc. Sometimes even if the screws are snug, manufacturing of the openings can leave voids or saw dust which can create a path for the air to escape, causing such noises. Axiom uses state of the art CNC equipment, so most likely this is not the problem, but you may want to check the seal and snug up the screws.

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