Hi, I have a 1998 Ford F150 4x4 with the 4.6 and just recently i notice this rattling noise . It sounds like it may be coming from engine, but i am not sure. The truck has 130,000 miles on it, and has always had excellent maiteneace done on it. The engne still has plenty of power and sounds smooth, but at idle makes this ratting noise. When it was idiling today, i gave it a little bit of gas and it seemed to go away, so that leaves me with the qestion of what it could be. thanks for any info.

 

Might be the heat shield underneath.

 

I hope that is all that it is. I did purchase a 5 year/ 100,000 mile warranty with the truck when i bought it. It had 118,000 on it when i got it, but i still hope it is not the engine.

 

The heat shield rattle is a pretty common problem on the muffler. You can either have a mufler shop tack weld it back on tight or have them remove it. If you don't do any off roading then you won't have any problem with it removed. It's only on there to protect tall grass from catching fire if it comes in contact with a hot muffler.