Does anyone know of any crossbars for a Legacy wagon that won't
howl/whistle when driving at speed?
Round ones make a lot of noise. Forget which brand but I've seen them
in a tear-drop or ovoid shape to reduce noise. The Subaru OEM ones are
horizontally flat to reduce drag and noise (but my Subaru with them
definitely has more whoosing wind noise than my Subie with no roof rack
at all). The Yakima bars that I had also had a windshield option that
you could mount on the front bar that would deflect the air upward but
it did produce drag. That changed the nature of the noise but didn't
eliminate it (I recall there was still a lot of noise after adding the
windshield but it was easier on the ears).
The noise is due to the turbulence on the backside of the round or
square bar. I forget where I got the clamps (they were probably
accessory clamps for the bar) but I got a couple of plastic or nylon
plates (something like 4x6) that I positioned horizontally at the
backside of the front bar and that reduced the noise. That eliminated
me having to buy a whole new set of the ovoid-shaped bars. I forget
what happened to the windshield and this was a cheap way to reduce the
noise almost as effectively.
If you have the flattened variety of roof bars but still want less
noise, the best solution is to remove them when you don't use them.
When you do use them, something else will be atop your vehicle making
much more noise and generating far more drag.