Dental floss mod
The dental floss mod involves inserting a length of fluffy dental floss into the middle of a keyboard switch's coiled spring to reduce the switch's noise.
The mod can practically eliminate a buckling spring's "ringing". However, it does not dampen the "click", which is produced by the spring itself when it reaches the "catastrophic buckling" state. (This can be demonstrated by pressing a spring/hammer assembly between thumb and forefinger.)
Each piece of floss should be as long as the spring it will dampen. A piece too short may fail to dampen ping, while one too long may also dampen the switch's sound and operation.