Took my (manual transmission) 2007 H3 over Medano Pass and up to some trailheads in Colorado for the first time. Generally performed well, but when traveling over washboard roads, I had really serious rattling under the car. I checked for loose skid plates, but all were tight. Dealer checked it out when I got home and couldn't find anything. Can this possibly be "normal"? Have never heard this before on pavement or less rough gravel roads.

Just for clarity on this, I never heard or felt this severe metal-on-metal rattling on pavement before or after, over 7,000 miles of summer and winter driving-no matter how harsh the pavement). Will investigate GM bulletin 07-02-45-006 in any case.