i have a 99 f-150 ext cab,4.6....i have something like a chirping sound when the truck is at an idle.sometimes it gets faster when i rev it up.it doesn't do it all the time...i thought it might be a pulley or something but i can't seem to tell where the noise is coming from.....anybody else ever had this mysterious chirp....thanks

 

It is a pulley. If it is increasing with rpms. Most likely an idler. If you pull the belt off you should be able to see if there is any free play in any of them.

 

I've had bird's make a nest in one of my exhaust pipe's and even around the engine. Rat's too, knew a guy that had a cat in the fan shroud.

Open the hood and let it out

Start with removing the belt then start the engine to see if the noise goes away. Stop the engine and turn each pulley to see if it makes a noise.

Most likely it the air compressor clutch if you have AC and the compressor could be on it's 9th live.

 

Iv had the belt make that noise too.
A Gator-back belt fixed it!

Phil

 

Check your harmonic balancer (crankshaft pulley) the rubber ring on mine deteriorated causing a terrible squeak and eventually it flew off one cold morning!

 

Ouch!

 

Jakehendrix, did you ever find the problem with the noise because mine is doing the same exact thing. I had the serpintine belt changed but it still makes the noise, not as bad though.