Hi guys! The idea for this mod came to me when I was playing around with a loose Model M keycap and spring/flipper. I noticed that when the spring buckles, the majority of it contacts a certain part in the keycap. So what I did was cut out a piece of a fabric band-aid and stick it in that spot like in the following image:
Here is a video of the resulting sound (First 2 keys are normal, and second 2 keys are modded):
In addition, you could combine this with a floss mod to eliminate the ping sound to create an extremely quiet buckling spring keyboard. I should note that this mod does slightly reduce the tactility of the switch. This should be able to be eliminated using a thinner band-aid, or cutting it so it does not completely fill in the recess.