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While walking around the airport on a windy day I occasionally hear a tingling or rattling noise from the engines of the parked jets. You can see the fans rotating in the breeze. What’s causing the noise? I should add that the aircraft are not in use, just parked with the engines uncovered.
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It's fan or compressor blades rattling loosely in their blade roots as the engines windmill in the breeze. The blades are attached to a hub or disc, and the retaining systems for the blades have to allow for thermal expansion, and also allow for a little bit of sideways compliance as the blades spin around, so they are a loose fit when cold. Compressor blades are usually in a kind of interlocking socket and fan blades are often mounted on pins that allow a bit of freedom of movement.
