This started couple weeks ago. While in the drive thru a squealing noise began under the hood. Sounded like a pulley bearing going out. So, I get home and look under the hood. I take the belt off and check for vertical movement of the pulleys. None is detected. However, the steering pump pulley has a horizontal movement and the pump itself is kinda rusty and so I change the pump and pulley. Replace the belt and.....still squealing. So, I change the belt...still squealing. I begin to replace the tensioner pulley and the other 2 idler pulleys....still squealing. Then, I replace the water pump...still squealing. Then, I go buy the shorter belt and bypass the A/C compressor...just to test....still squealing. The last and only thing left I can see is the alternator pulley....I've got a good used alternator and plan on putting it on, just to test....bet it still squeals. Any clues as to what's left that can still squeal? I don't know of anything on the crank pulley that can squeal. The odd thing is....no matter the rpms...the squealing is always the same level and speed. Whether idling or revving the engine....and it's sporadic. I haven't been able to pattern anything about it. I looked back on this forum for last 4-5 months and didn't see anyone with this issue, so I decided to post and see if anyone else has/had this problem. Apparently it's not serious, I've put 700/800 miles on since it started. I've got 2 extra belts and all new pulleys!

 

Here is a sticky that I have started that might help a little...there are more things to add as I come across them. If you find a solution not on this thread pelase let me know and I will add it to make it as complete as possible.

https://www.f150forum.com/f12/engine-whistle-17415/

 

hey i had the exact same problem, i took it in to Ford and they said a bearing in one of pulleys was loose or something like that, they changed all my pulleys and gave me a new belt and it all gone. If your still under warranty take it into a ford dealership and they'll fix it right up.

Cheers