I have a metal on metal rattling noise from the front of the engine that started about 4 months ago it was very faint at first but is loud now. With the truck in park if you rev it up the noise gets very loud!! I checked all the pullys and the idler pully was a little loose so I replaced it but the noise is still there any help would be great!

 

get a hose hold it to your ear and start searching! Have someone hold the rpm's where it makes the noise! You can also remove the belt and do a quick rev and see if it's still there if not it's a belt driven part!

 

That worked took off the belt and found the noise it was the fan pully thanks for the help