So, I live under the approach path for an international airport. Planes are flying over my house on final descent all day long.
After I moved into my house, I noticed an occasional weird sound, like pipes groaning under pressure. Eventually, I realized I could hear it outside too, and that I only heard it when there was a plane in the sky.
Turns out, the sound is poorly-oiled landing gear being lowered. The metal-on-metal grind is so intense that I can hear it on the ground from more than half a kilometer away.
So... I decided to start keeping track. So far, two thirds of the planes that exhibit this are flying for Spirit Airlines.
So, I guess the lesson here is: don't fly Spirit.
@LouisIngenthron It might actually be pipes (well, the hydraulic hoses) making the noise. Low-cost carriers like Spirit tend to have fleets of very uniform composition, so if that model normally has loud landing gear you'd expect to hear that on nearly all their aircraft and a smaller proportion of mainline carriers'.
@khird Maybe, but I've don't think I've ever heard hoses make sounds that could be heard that far away. It does sound quite a lot like metal-on-metal.