2007 Ford Ranger - Rattles

My truck has 133k miles and never had a major issue. The other day, something started rattling when I accelerate or decelerate. It sounds like a large washer loose on a bolt rattling as the engine vibrates. I got underneath it this weekend and touched and wiggled everything I saw. Nothing seems to be loose. Any ideas?

Although nothing seems to be loose, Owould still suspect the heat shield.

Thanks, Purebred. I’ll get back down there and take another look at the heat shield.