mounting makes a difference
SX, Aeromotive, and Paxton are LOUD. My solid mounted blue Paxton pump is louder than the ATI blower on my Mustang from inside the car
Weldon are higher pitched I'm told. If you mount them so that they are isolated from the body they will be quieter but this kind of mount can be difficult to create. Mercedes makes some rubber isolated mounts intended for an airbox that I've been told should isolate the pump well - I've not yet tried this. I think other companies use similiar mounts but the Mercedes units were highly recommended, apparently they don't use rubber that can detriorate quickly.
IF you solidly mount it to the body it will use the metal panel as a resonating board - like a violin or guitar does. Dynamat on the panel WILL help dampen this sound but not enough to really matter if you're in the car - trust me!
Lastly, as I discovered on my project car, the braided line itself will hum and vibrate like mad too! My car's line vibrated like a guitar string and anywhere it touched the body (bad!) it transmitted noise. Even my regulator couldn be heard when it wasn't isolated! Adel rubber cushioned clamps and careful routing will mostly fix the problem with the braided line as will rubber hose slipped over it on contact points. That pump is a Holley Blue pump that's nowhere near as loud as the high end EFI pumps but it was driving me crazy with all the noise. That car has full Dynamat, more insulation, and full carpet too. It's amazing how the sound can travel.
