When idling and just barely accelerating, I get a bad rattling sound (kind of sounds like metal rattling) coming from the driver's side, sounds like it's near the rear side of the engine, and sometimes the truck sounds smooth, but when the idle changes (like when it's cold), I get the really bad rattling sounds, but then when it idles back down, it sounds smooth again. This sound is worst between 700 and 1350 RPMs. I don't know what to check?

 

Sounds to me like you are another victim of the cat sheild plate rattler. Mine did the same think. Wrap a clamp around the front catalytic converter and tighten'er up. No promises but it fixed my rattler right up. Hope this helps.
-Landon

 

I'll check up on that. Thanks!

 

I'm glad I checked the engine section, I've been annoyed with this rattling on my truck that sounds just like you described, but have been unable to find the cause. I haven't looked yet but I'm sure that is what it is. What kind of clamp did you use? A large hose clamp?

 

pickupman, Piston Slap? what kind of engine/miles? what kind of oil/oil filter?are you using.

 

Yea a large hose clamp is what I used. I had a buddy that used a large vise grip until he could get a big enough clamp. I don't recommend this because it could come off and fly through someones windsheild. And yea he is an idiot. I didn't know until after the fact. If you cannot find one big enough then throw 2 together and get'er done!
-Landon

 

03f150man, it didn't start until after I had 110,000 miles on the truck and then parked it without even starting it for 18 months. Now it has about 130,000 miles, and I use Valvoline Fully Synthetic 10w30. It really sounds like it is something external, though, definitely sounds like it could be something in the exhaust.

 

Could you be hearing predetonation/pinging? I have heard people descibe it as sounding like a marble in a tin can.

 

The rattling should sound like it is coming from the back of the engine because the first catalytic converter is in the bend where the exhaust turns from a downward slope to moving toward the back of the truck. You may have to climb under there after cranking it up in the morning and see if you can stop the rattling by squeezing the catayltic converter with your hands(not recommended after the engine warms up). Look, listen, and feel. Mine only did it when it was at a warm idle so when I would crank it up it wouldn't do it. But once the idle came down it started rattling. I had to check from different agnles to make sure I heard it from the right spot. Ford has had problems with this. You guys aren't the first and won't be the last. Hope this helps.
-Landon