Cutting down pump noise

[wetcoast]

I have two pumps, a Reeflo Dart underneath my stand dealing with a Closed loop which isn't _that_ loud, but I also have a snapper in my "equipment room" / gutted bathroom that is making obscene amounts of noise even after a warranty replacement. I've heard that taking off the endcap and adjusting it to ensure the fan blades do not rub is a good technique, but I want to drill down deper and cut down vibrations. I'm using styrofoam right now which is ok, but I think I can do better, like a big block of rubber. What are other techniques people are using, and where are you getting these materials? I can't for the life of me find chunks of rubber.