Clicking noise... Help!!!

[LongNLowGMC]

So a new little annoyance has popped up on the GMC and I'm no mechanic by any means so I'm hoping maybe you guys here could give me some direction. The noise itself is a clicking/tapping that slows down as the truck slows down, kind of like putting a baseball card on the fork of your bicycle into the spokes. Once it's at a stop it's quiet, only does it when it's moving. It seems to be coming from the front passenger side, it only does it when I am slowing down and starts around 30 mph until I stop, don't hear a thing once I'm at speed. It can be quiet, it can be loud sometimes, sometimes it goes away completely. And I've noticed twice now if its doing it and I drive over something bumpy, like railroad tracks, the noise will stop. It doesn't matter if I am braking or not, even the truck is just rolling slowing down without the brakes it will do it. I took it to a guy in town and he gave it a quick look over on their rack (they were closing) and said the only thing he saw wrong were the bolts on my fender wells were all loose and missing a few, I've replaced and tightened them all down and its still doing it (I really didn't think thats what was causing it so I wasn't surprised).

Well that's about the best I can describe it, so what do you think? Any thoughts or ideas are appreciated, thanks guys!