My 99 F150 5.4L has started making a very loud, low-pitched whinning sound from the engine. It sounds like it's coming from the passenger side, top of engine, but I'm not 100% sure.

I was certain it was the idler pulley, but after the swap, the sound is still there. So, I removed the belt and started the engine. The sound remained even with the belt off.

Some more specifics for anyone that may have experienced this:

- Engine is quiet at cold start; sound develops only after engine is warm
- Whinning sound occurs when engine is at near idle RPM's; goes away with throttle
- Occurs in park, neutral, or drive

Any advice on what I should check next (short of taking to the dealer) would be most appreciated.

Thanks.

 

Check for vacuum leaks. Namely, the pcv elbow where the pcv hose connects to the intake.

 

While your looking at that pcv elbow go ahead and replace the pcv valve. When they get nasty they start buzzing. I had no clue about this until about two weeks ago. My truck made an annoying buzzing sound at idle that would wind down after I shut the truck off. I did a search for "buzzing" and came up with bad pcv valve. I had my doubts but I replaced it anyway and I'll be damned if it didn't work.

 

Thanks Chester and GearJammer!

You guys were right on. Replaced the PCV valve and the elbow. Problem solved.

Thanks again.