A bell-type cover over the air filter (one that covers most of the actual filter element) will go a long way to attenuating the hiss of the air being sucked in. That is what I put on mine, and for the same reason as you state -- attenuate the hiss. The cover I show here only cost me about $30, but you can spend a lot more if you want. The cover I use has a 7" diameter circumference and a 2" depth, which fits very nicely over the 5-1/2" K&N air filter supplied for the Cobra air intake I bought.