It would "grind" in a manual or "stick shift" if the synchronizers in the transmission were not aligned properly when shifted. The shocks may be faulty when you hit a bump the tire may hit the underside of the fender well. Hope this helps.
I would need more information on when this is happening. Are you shifting when this happens, or braking, or just driving along with no gear changing or anything?
Grinding when shifting could be an issue with the transmission.
The grabbing over bumps when you're braking can be normal in a truck because of the lightness of the empty truck bed. When is bounces in the air, it feels like it's grabbing because one of the tires is not connecting with the road surface. Hope this helps.
〉 Answered on Apr 21st, 2008 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines