Alternator Noise? Bearings?

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Harbor freight tool makes a mechanic stethoscope that is well worth the money, but a long screwdriver works to pinpoint noises if you keep your pony tail out of the fan and belts.

Remove the alternator and have it bench tested at most any parts store. I bet spinning it by hand will feel wrong with all that racket.
 
Yank the belt and spin the alternator by hand. You should be able to hear/feel if the bearings are going. The choice is up to you. Reman alternators aren't all that expensive. You can also convert to a junkyard 3G unit. If you're mechanically adept, you can just replace the offending bearing(s).
 
Yes, rebuild kits are a good option for some folks. They are the ones who feel better knowing they did it than having a lifetime warranty from someone at a mass rebuilders. One dealership I worked for wanted to do it this way every time a kit was available. Except for brake parts that might have rubber seals that have been sitting there for 15 years, I usually just buy a good brand re manufactured part and get back on the road.
 
That doesn't sound like the typical bad bearing to me. More like something slapping or rubbing against something else. Make sure one of those gigantic blades of straw under your engine isn't the culprit first then look for other sources. Possibly even an exhaust leak? I hear a slight miss in your engine and that sound sort of goes along with it so I would check for a leak where your exhaust pipe mounts to your manifold or header. Your RPM is a little fast too so you might slow it down a little also. May help it narrowing the source down