2001 F150 4.6v8 rattle from engine

I have a rattle from what i think is the accessory belt area. i am wondering if it might be the bearings on the idler the water pump or the alternator. I does not happen all the time but always does seem to appear after running for 30 minutes or so. Sometimes it will start immediately i start the engine.

I have been listening to this with a tube and think it souds like its coming from the alternator, hence i suspect the bearings. Has anyone changed the bearings on an alternator? Any idea of part number?

Replaced the alternator and the noise went away! Must have been alternator bearings. I do look at replacing them but difficulty in determining what was needed plus not having a puller to get the alternator apart led me to do a simple replacement of the unit.