Mine was doing it from the driver's side manifold shield - it has become flexible over the last 4-1/2 years and started rattling away around 2800-3300 rpm while accelerating and wouldn't stop until in the next gear. It did this in first through 4th, (probably 5th and 6th, just never noticed with the rest of the wind and tire noise)

 

Here are two pics of what I finally found almost directly in the middle of the frame. Two of my weld tabs had come loose, so I hose clamped them. So far it seems to be working pretty well.

 

My welds started going as well. How long til the muffler shield goes I wonder

 

...I have the same issue. The metal rattling started just on acceleration and has since increased to heavy rattling on start up. Glad to see this thread and will get under the Jeep to inspect. The rattle is driving me crazy.

 

More than likely the exhaust cross over pipe heat shield. Happened to mine and I just put some metal strap clamps on it

 

Please excuse my ignorance, but where in the engine compartment is this? Should I look from the bottom up on the driver side?

I have the same rattle and it is starting to annoy me.

Thanks.

 

Its the crossover pipe in the center of the truck underneath.u need to crawl under it.

 

I second the clamps on the crossover shield, I even checked all of the welds and they all were fine and wouldn't pry at all. I strapped it for giggles since I bought the clamps and my rattle went away (only to be replaced by a suspension clunk, ha)

 

What they said.

 

What clamps did you buy??

Thank you!