I just picked up a 96 4runner LTD. It didn't do anything on the test drive and seemed perfectly fine.

I bring it back and now once the truck is warmed up, there's a rattle. When in the cabin, the rattle comes from the rear around the cargo area. Then I went to investigate outside the cabin and followed it to the front engine area.

I'm thinking something got loose over time, and is now really close to something that heats up and expands.

This only happens when the truck is in drive.

Does anyone know what this could be?

 

id start by checking the exhaust system from front to back. make sure no heat shields are rattling, in contact with anything, etc. etc.

what kind of rattle? plastic rattle, metal rattle? that would help us alot.

 

Rattling definitely sounds larger in size. It very well could be the exhaust. It sounds like it's metal on metal, but it's not raspy. It's more thudy...

 

check motor mounts.

 

Hmm ok, I know on a camry, you just hold the car with the brake, give some gas and watch the motor. I'm not sure what to look for though.

 

well just find them and inspect them for cracked rubber, etc

 

im almost positive it's your exhaust. I had the same problem, but mine rattled at exactly 1500 rpm. It was determined to be a loose exhaust shield. It would only rattle in drive b/c of the increased load on the exhaust. good luck