Loud 'rattle' and 'clanging' noise on cold start up - Is it normal??

Hi everyone. These diesel's are new to me so im still (slowly but surely) learning more and more about them.....thanks to all you!!!!

My 2003 wagon, on just a couple of the past cold mornings, has had this crazy loud rattle and clanging noise going on. I dont think its the normal diesel engine racket. It will come and go every few seconds and only last a few minutes. On warmer mornings it does not do this. The only thing I have noticed lately is the the battery light has flickered on and off every once in a while....so could this noise im hearing be the pulley on the alternator??? This rattle isn't consistent when the battery light flickers though....wish it was so I would just about know for sure that it was the alternator. I have another alternator I will be putting in it soon. Im hoping the find that the pulley on the alternator I take out has lots of play or something. This is a hard one to pin point because of its short duration.

Has anyone experience something like this or is this something normal???

Thanks!!

Disconnect the acc belt and start it, if it goes away then spin by hand the alt pulley, it should spin in one direction and freewheel in the other and be smooth.

Better yet, take the belt off of the alternator, block the fan inside the alternator with a screw driver and by hand, try to turn the pulley in both directions. It should not turn in one direction and turn smoothly in the other direction.

If the pulley is bad, you can get a new pulley and the special tool to change it from one of our vendors. IIRC, the pulley on an ALH can be changed witout removing the alternator.

If I block the fan in the pulley why should the pulley only turn in one direction?

So I picked up an alternator from the wreckers and its pretty much exactly the same as the one I just pulled out except it does not have the clutch/pulley. All the same plugs on the back, etc and the wreckers say the part number is for my jetta. It just has the regular pulley. Can i put this on my TDI?? Out of the dozens of alternators i have changed over the years on all kinds of cars(except vw...lol) I have never seen this clutch type pulley on an alternator.