I personally would start with replacing the cherry brown switches. If you're getting spring ping, you can disassemble the switch and replace the spring or try lubing it. Me? I would toss 'em and grab some other higher quality switches. You could also swap the springs you already have for some Sprits or something but it's probably not worth your time imo.
Adding foam or silicone could certainly help muffle the noise but since that ping is likely happening in the key switch and your keeb is hot swappable, I think that's the better way to go.