I wouldn't rule out the A/C, typically a failing A/C clutch or bearing will actually make more noise when the A/C is off.

Try turning the A/C on and see if it goes away or gets quieter.

Here's a list of the pulleys,

Upper 5L3Z*8678*BA $26.10
Lower 5L3Z*8678*AA K $25.01
Tensioner BT*85* $61.31

Don't forget the 5% coupon code "f150forum" if you order n our website.

-Steve

 

Thank you Steve. Is the ac pulley replaceable? Only reason I ruled that one out is cause I had the ac redone under warrant a few times a couple years back. They replaced pretty much every part of it because it was making a screeching sound when that pulley was engaged.

 

Yes it is, it's three pieces. The pulley, field and disc.

In most cases you're best off replacing all three if the pulley goes bad, runs about $115-135 depending on build date.

-Steve