noticed this high pitch sound a while ago, but seems to be louder now than before. it makes the truck sound like electric car. doesn't seem like i lost any power and the mileage is the same. truck runs great, but this sounds bothers me.
it's there when the car is in park and i rev it a bit, so nothing to do with bearings, but could be belt or anything else. anyone experienced this before, please give me some pointers where to start.
thanks

2007 f150 fx4 5.4

 

Sounds like alternator whine. Get your battery load tested.

 

found few videos, sounds like Bad Idler pulley

 

That's also possible. You will need a stethoscope to pinpoint it. I would still load test the battery, if it's original it's time.

 

changed the battery 2 yeas ago

 

All it takes is 5 minutes at Autozone - you do need to rule it out. I've seen batteries fail early.

Another thing to do is temporarily remove the serp belt and fire it up for a minute to verify it's something belt driven that's whining. If the whine is gone, shut it down and spin all the pulleys by hand and see if any of them "feel" sticky or rough.