Rubber tubing will eat up a lot of the vibe from a string, and it weighs quite a bit. You lose quite a bit of speed, but sometimes the stealth advantage is nice. I'd rather not have a tube to break and dry rot and so forth, so I think you made a great move.
Cat Whiskers should have done the trick. I use them myself and nothing works better for the minimal price they have. An STS or other type string stop works wonders also, but they carry a heavier bill also, and you need to monkey with them a bit to get them just so. Not a big deal, just something to be aware of.
Are you 100% sure that its just string vibe and not something else on the bow? Quiver bracket and sight fastners are notorious offenders.
Push comes to shove and you can't figure it out... I'm at Wilcox in Newport News... carry it by I'll be happy to put the whop chuey on it.