Originally Posted by
coldfeet
Add something that makes even more noise, like those tailpipe BRRAAP things, to drown it out? It's probably some wind buffeting that is strong at a particular frequency and you have to change something in the airflow to break it up. You have all probably experienced where you roll down a car window a few inches at moderately high speed and there's a loud whump-whump air noise, but when you either roll the window further down, or partway back up, the noise decreases. There's no obvious way to tell which change to make to the rack (short of a wind tunnel) - the paracord idea is nice because it's easy and reversible.