I seem to have developed a rattle. It happens mostly on cold start ups. It's not piston slap. Now i'm not much of a motor head so go easy on me. It seems to be coming from one of the pullys that the serpentine belt is connected to. Could a pully be going bad. It seems to quiet down a bit when she warms up. I also hear the rattle at a much quiker pace when I am at higher RPMs just before it shifts gears. I would just like to know what it could possibly be before I take it somewhere to be looked at. Out of Warrenty, oh well. I have to say this will be the first bit of repair work besides the normal upkeep. (78,000) Not to shabby.

 

Check out this thread :

https://www.f150online.com/forums/sh...e+before+shift

I know you don't have a Lightning, but it sounds like similar problem.

Mike