Thanks for your input. I've been talking to a few people and they made an interesting suggestion. Perhaps the flow into the icebox (from just below the bumper) is being restricted. I've heard of people cutting holes in the bumper area to increase airflow.

I've also noticed that the sound stops when I'm making a right hand turn. The air is coming in from a different angle at that point. I'm not sure if it relates.

The icebox is supposed to be no louder than the stock intake system. What do you think?