constant strange noise in the engine on 2002 GMC Safari

constant acute sound when I start the van, it doesn't stop, I replaced the serpentine belt, the alternator was repared,the water pump is not the problem and the sound continues,

Asked by for the 2002 GMC Safari
It depends on what kind of sound you are talking about....

If you are replacing alternators, belts, and water pumps, my guess is that are trying to find a whirring noise of some sort...

Without any other info and without a good description of the noise, my first advice would be to check your fan clutch. There are a few different types and various ways to test them. If it is the mechanical style fan clutch, it may or may not be thermostatically controlled.

Let me know if this is the noise and if it is, we can look into how to fix it.