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Most shrill sounds are associated with belts, might be caused by different things: slippage due to exposure to liquids (coolant leaks, etc.), over or under-tension, etc. Cheapest option would be to change the accessory belt and see if it does make any difference.
In my opinion, water pump bearing failure is caused either by too old pump (and the rest of the components, e.g. the belts are likely to be as worn or break before that happen), or by incorrect belt tension so unlikely to be that. it could be the water pump that leaks and cause exposure of coolant on the belt so worth checking the water pump if possible. Alternator pulley is a "complex" part and not always sold separately from the alternator, but I'm not sure it is associated with failure usually so I would check the accessory belt first. What's the car/engine?
paulbiche-
Micra 09 1.2 - Oh I can see where your coming from, the car runs vbelts and the tension seems fine by the can turn the belt 90 degrees on the longest run trick, tried the increasing the battery load too see if the noise increases or decreases. It doesn't.
Tonight am going to have a poke and see.
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Had a poke, there is play in the water pump. Enough to feel but no water leak. No play or roughness in the idler bearings nor the alternator.
lynx
Ok here is one for you.
Squell/shrill noise that goes up with engine speed. It is in the area with these so what could it be:
-Alternator;
-Alternator idle bearing;
-Water pump;
-Water pump idle bearing.
Place your bets.