Is it 'shaking' on some sort of mount? Or is the unit, itself, making a lot of noise?
I mean, perhaps there is some type of rubberized mount that you can buy to help with this. Perhaps contacting the mfgr. for info. I know there are rubber mounts for grinder pumps and such that make a lot of noise when mounted directly on a concrete 'pad', steel plate, or something. Othere than that, perhaps the unit needs to be serviced if the 'noise' is coming from the unit directly. If this is NOT the case but the noise is 'normal', then you're left with 'gathering ideas' on how to do as you ask - ie., sound insulation.
ONe more question - Describe the complete set-up of the pump. (Base, boxed in with what (if anything), etc.)