Has anyone tried a rubberized coating on older Klipsch tweeters?

Thanks !

Not tweeters, but I have used a product similar to dynamat,  peel-off rubber like sheets meant for this purpose on the outside of the horns on my Epic CF-4's. I did 2 layers and it was effective, but I wasn't having an issue with brightness, I just wanted to make it more dead, and to compensate for the fact that it's plastic, not thicker wood.  

Thanks roxy54!

Dynamat was the material I used as well. 

I have used Dynamat on the outside of the horns in some of my Klipsch Heresy speakers.  I'm not sure I'd bother with the RF-3s.  I'd encourage you to move to the Heritage line or see if you can find some second hand Epic (CF-X) or Legend (KLF-XX) series speakers if you want better sound quality and like the Klipsch sound.  Bob Crites sells replacement tweeters for Klipsch speakers that are less fatiguing, but I don't think he carries anything for the "Reference" line.