In my experience, replacement parts that are not to the correct tolerance can cause this type of incurable squealing. For instance, the pulley on the replacement water pump or some other replaced part (i.e. alternator, air pump, etc.) may be out of line with the other pulleys, creating an off-center rubbing and squealing.

If this is the cause for your squealing, there may be no cure. I had the same problem on a Ford Escort I owned - Pep Boys water pump pulley protruded about 1/32 of an inch further out than all the other pulleys; not much, but enough to result in an incurable squeal. Even the belt dressing from Auto Zone wouldn't help.

Is there any black "dust" around the pulleys? Look for the faintest trace - it is actually rubber worn off the belt due to the off-center squealing. If so, there's nothing you can do outside of replacing the out-of-spec part and you'll just have to learn to live with it...

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