Well, I've...

observed alot of hairsprings expanding and contracting and I've never notice any of their coils "ringing as they hit each other". I guess it's possible though. However, in most cases of ringing the coils might not actually be hitting each other, but, rather, the entire coil might be vibrating in resonance to other vibrations being produced elsewhere in the movement. Naturally, I would suspect any spots where there are impacts taking place. The two places I would suspect the most would be the contacts that takes place between the escape wheel teeth and the pallet levers.

technoguy