I have a new Jamis Sputnik fixed gear bike. When ever I go over a larger bump the headset (or at least it sounds like the headset) makes a vibrating sound. It doesn't make the sound on smaller bumps, but I have a fairly bumpy commute and it's driving me crazy! I've checked the headset (twice) and it's tight, there is no play in it at all. If I lift the bike up and drop the front wheel it will bounce and recreate the noise. I've never had a bike make this noise, and don't think it's normal, nor does it sound good. Could the headset be set wrong? Cheap headset? Is it normal? What's up! Any help appreciated.

*I found one other post which sounds like the exact same problem, I thought it interesting they also had the problem with a fixed gear.