I am going to take a stab at this because it happened to me.
I have the chrome package with the crossbows as well. The dealer had the crossbows installed in a funky way. I also noticed I had tie hooks up there too which is what I think was making the noise. If wind whips through that tiny hole, I'm betting that's the whistle/buzz you're hearing (if you have them). I haven't seen many H3's with those on there, so not sure if you have them.
I have my crossbows as follows. The back one is slammed all the way to the back. The front one is all the way to the front (to the point where you can lock them back). The brochures had them that way. The dealer had mine originally about a foot off the front and slightly behind the back door. No whistles now.
Give it a shot!
BTW, I am amazed on how well the crossbows work and how easy they are to slide around for adjustments. Good investment on my part!
