Why do doors creak?

Dave - If you have a door which is getting a bit old, getting a bit rusty and you haven't oiled it properly, you get a very similar thing to brakes squealing or in fact, dragging finger nails down a blackboard. It's to do with stick and slip. What happens is that you get quite a lot of friction and there's a lot more friction when two things are stationary than when they're moving. So, essentially the two bits of the hinge lock together, then the hinge bends a bit, and then the force gets enough for it to break, and it jumps forward a bit and then it stops, and then it bends a bit, and it jumps forward.

This jumping can happen at a range of pitches, including the horrible 50-100 Hertz range. As you're getting jump, jump, jump, jump, what you hear is this horrible creak noise.