I have a 2000 F150, 4.6 with only 206 K on it. Fantastic truck and no complaints. A squeek developed with the serpentine belt between 1200 and 1400 RPM's and it's a constant squeek at 1400. Figured it's time to change the serpentine and tensioner as tensioner is OEM and serpentine had 80K on it. Did that with no success and the squeel appers to be getting louder. Anyone out there have a similar situation before I bring it to a shop. The only thing I noted was that the crankshaft pulley has a slight wobble at this RPM but nothing else was noticeable.

Thanks

 

It could be alternator bearings or some other accessory making the noise.

 

I'd investigate this closely.