Must be something wrong somewhere as I found these pumps to be the quietest pumps around!
Have you got both outputs in use? if not, make sure the one you aren't using is blocked or that it is linked to the one you are using with a T-piece.
Use silicone airline, and make sure the rubber feet are on the pump and that is is on a firm level surface.
Another thing to check is where your airstones are in the tank and if they are resting on the glass etc. IME the worst noise from an airpump comes from the airstone itself (I used to have a cheap bubble wall that made a horrendous noise, but when I changed to a hagen aircurtain using the same pump and airline etc, the noise levels halved!!)
After that, then yes a couple of air valves (just the type that squeeze the airline will do fine!) will reduce the noise.
