For the past several days I've gotten this rattling sound coming from under the bed of the truck. Oddly enough the rattling seems to be related to the speed of the truck and wind speed/direction, leading me to believe that something is loose under the truck and the wind is causing it to hit the bottom of the bed.

I looked under the bed as best I could and didn't notice anything out of the ordinary. It sounds like rocks or pebbles hitting metal but it isn't being caused by anything being thrown up by the tires. Really strange. I'll probably wind up taking the vehicle to a mechanic but thought I'd post here first. Any ideas? Thanks in advance....

 

Check your rear shock bolts for tightness, particularly the upper ones. Don't just look at them, but place a wrench on them and check.

 

Could be the heat shield on your fuel tank. Mine worked it's way loose and vibrates unless I crawl underneath and readjust it.

 

Yep, that's what it was. Part of the heat shield attached to the fuel tank had come loose and was hitting the driveshaft when the wind was right. I hadn't noticed that on first inspection. It appears that the nut securing that portion of the shield had worked its way through the material, leaving a large hole, which will necessitate a big washer to cover it. Not having the proper hardware on hand I improvised a method, using a rope to hold the shield in place until the proper hardware can be found.

The photo below shows the improvisation. I also added a tie-wrap that secures the rope to the bolt so that it can't slide forward or backwards. I'm curious why a heat shield is needed here in the first place, since the heat producing components are a pretty good distance away?