Your best bet is to head to Sears or Harbor Freight and pick up a cheap mechanic's stethoscope.

Touch the end of the scope to the center of the idler and tensioner pulley (non spinning part, then touch it to the alternator body, power steering pump body etc... You'll definitely hear which part makes the noise.

The scopes I've seen at Harbor Freight are under 10 bucks and are definitely a must for any DIY'er to have in his/her toolbox.

Because I have now done this job, I would say do the Alt at the same time - if you know it has more than 70K miles on it. Yes, it will hurt your wallet, but so will being stranded somewhere if you can avoid it.

As far as price goes, I would get a quality reman. As posted before, BMW will also sell you a reman - not a new - alternator, but theirs will be three/four times the cost.

My alternator went at 126,000 miles. I didn't have much choice when it occurred but to have the dealer replace it. But I wish I had gotten a lifetime warranty rebuilt from AutoZone for $386 instead of the $832 BMW unit.

2002 X5 3.0 245,300 miles
2004 325i 109,000 miles

I got the tensioner pulley and idler pulley on the way, but decided to leave the alt in till the summer. (hopefully it doesn't fail any time soon) Going to do a complete cooling system overhaul so I'll leave it in till then.

I noticed when I accelerate my headlights dim a bit. Would that be signs of alt going + battery going bad as well ? I've left my X in the garage for days with very cold weather and it starts right up. . . .

Speaking about cold weather, I started to get that yellowish crap in the oil cap. Been cleaning the oil cap and valve cover CCV hose with a rag and a bit of WD-40. Going to avoid short trips.....

Suggest you have the battery load tested at a local auto parts store. Most will do so at no charge.

You can also unlock the cluster and monitor alternator output.

If you buy a reman alternator, have them test it before you install it. I installed 3 remans in one week before i got one that worked.

At least you didn't have to do the same thing four times and get the same result. What brand was that?

It was a pep boys reman. I finally got a refund and went to carquest and the first one from them worked.

Hopefully is not the Alt. Just got the rest of the parts I ordered today . Going to tackle this tomorrow.

Hope you end the year on a high note.