My normal camera is horrible when it comes to sound. But I found that by taking a peice of pool table felt and putting it over hte mic and then putting some electrical tape over that cuts down the wind noise greatly. Without it my camera sounds way worse than yours. Just stop by a local pool table store and ask them for some "simonis" trash cloth. You don't need much and I'm sure they'll let you grab a peice out of the garbage. I've done foam before but I felt it killed too much sound.
Here is mine and this was on a very cold and windy day.
http://www.youtube.com/watch?v=UffB6Yt6aR8
When I get my GoPro camera back from warranty (if they fix it) I'll mess with some sound deadening for that camera and let you know. Especially since I hope to use it for my triathlon which will have me on a road bike where you hear all wind clear as day.
You could also try mountain it underneath your tail if you feel the tire won't crush it when it compresses. Or throw on your stock mud flap and have it facing backwards there. That should keep some wind off
Plus did you have the waterproof casing on or not?