Why is my engine squealing?

I drive a 2000 Ford Mustang v6. The engine was making quite a bit of noise while driving, so I decided to replace the serpentine belt. However, I noticed no change at all in the noise. Also, the squeaking continues for a short time even after I cut the engine and the serpentine belt stops moving all together. Leads me to believe it isn't a belt or bearing issue, but not sure what else it could be. Any help would be greatly appreciated!

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Squeaking - could be a mouse. Squealing - could be a pig. Or anything that continues to move after engine is switched off such as the electric radiator fan.

If it continues after you kill the engine, the only logical source of the sound is the cooling fan(s).

Could be a vacuum hose that is off and whistling. It would continue for a short time after the engine has stopped as the vacuum fills

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