i've had exactly the same problem once before fella, i think it was finaly put down to the back half of the pully had seperated from the shaft it sits on (not the alternator shaft the center of the pully itself, the part with the keyway) and was slowely working its way backwards. i only noticed when it started to eat my alternator too. the only fix i was sugested was to get a new pully!

have a look at it tho and see if you can see any signs of movement. or any play in the alternator bearings in or out.

steve

Thanks Steve,

Turns out there was a washer behind the pully, which has 'ground' itself into the alternator shaft. This had worn the washer down, allowing the pully to move back had 'graze' the alternator casing!
I ordered a new pully, to be on the safe side, but the one fitted is a cast type, which I haven't seen before, and its better quality that the new 'repro' that's come through!

At least it's not a collapsed alternator bearing, which I first thought, it's only done 4K miles!