I have a 2008 F150 Limited 5.4L about 205k on the truck but 130k on the engine. Truck ran fine all weekend, sat all day monday, went to start it up tuesday and heard a loud squeal. It gets softer after 10 seconds or so but never goes away. Its not a whining noise but more like a squeak, chirp or squeal. Ive heard it could be many different things like the belt, belt tensioner, idler pulleys, alternator or even water pump. Does anyone know the best way to go about eliminating these options? I posted a video of the noise. Thanks guys

 

If you watch the belt, does it seem to be wobbling? I would check the grooved idler pulley on the driver's side. Mine went out on my 07 and I couldn't get it fixed for whatever reason.

 

The belt doesn't wobble at all. Is there a way to check if the pulleys or bearings are bad? Can you tell by free spinning them? I have a new belt so I'm going to change that either way.

 

I just took the belt off and spun the alternator a little bit and the same sound (a little whistle), only a lot less loud, is coming from somewhere inside the alternator housing. I think this could be the culprit.

 

Sounds like you found your problem. I'd go ahead and spin the other pulleys and make sure they're all quiet, then put the belt on and make sure the sound is still there. Then try to get closer to the alternator to see if the sound is for sure coming from there while it's running, being careful not to hurt yourself of course.

 

The cheating way, being, of course, to record a video on your phone.

Announce "Here is the Alternator" put it close to it, pull it away, put it close, pull it away -- do this for all pulleys and see which one sounds the loudest as you get near it.

 

before you change Belts.. hit the alt pulley bearing with some WD-40 .. see if the noise goes away..you don't want WD-40 on where the belt rides on the pulley.

 

Im gonna try the WD-40 tomorrow. I swapped out the alternator and the noise had lessened tremendously to a very slight squeal when I'm on the gas. Its only enough to hear if you have your head under the hood. I think the belt tensioner pulley is rubbing on the ?engine block? or whatever is right behind it. There are wear marks cut into the metal behind it. Idk how long they've been there though. Truck is running fine now so I may wait until next week to tackle that. Unless anyone thinks its a problem and needs to be fixed asap?

 

May last a day, month, year... sounds like tensioner failure. I'd definitely try to do is as soon as possible.