I posted this in the Ride Reports section, but thought I'd put it here, too...  any thoughts on reducing lateral "wagging" back and forth of Planet Bike plastic fenders at high speeds???
 
 

 
 
The front fender has a ~8" long unsupported extension past the frame attachment tab, and when I would hit ~20mph or so, or into a heavy wind, this section vibrates back and forth like crazy... .  When I got home and took the fenders off, it looks like the edges of the fenders had been contacting the tire sidewalls whenever they vibrated like that, because the sidewalls were discolored with whitish dust (ghosts of fender use past, from the inside of the fender.).  If that's the case, I'm glad I didn't blow out a sidewall!!!!    
 
I actually had the "front" fender on backwards, to give more coverage toward the front, and the extension closest to me was vibrating -- and when it's on "regular", that same section vibrates when it's pointed forward.  Any thoughts on how to eliminate this effect on Planet Bike plastic fenders?  Cut away the "cupped" edges in that section, to reduce air capture?