Originally Posted by jerrymcdougal
HAHA, no actually its from the prawls in the rear hub. Higher end hubs have tighter tolerances and everything fits super super close. This makes a hub very sturdy (as far as the prawls go) but also very loud. The prawls snap back really hard creating the noise. Some people love that sound as it is the sound of quality, others like yourself hate it. You may be able to quiet it a bit by lubing the insides of the hub, but its just fine how it is.
Edit: beat me to it maddmaxx!
Actually Chris King and DT/Hugi hubs, arguably the noisiest of the rear hubs, have no prawls. A pair of spring loaded ramped discs work against one another to provide the freewheeling function. Very simple, very positive, and very loud.
Oh - they don't make that noise if you pedal the downhills. I'm not sure that we're even allowed to sell King hubs to people who coast downhill so you may not be qualified to buy that bike.