The squeal you are hearing is most likely the belt. It either needs to be tightened or replaced. You can try some belt dressing sold at auto parts stores if the belt is tight and in good repair.
If that's the extent of the complaint, check the serpentine belt and tensioner.
Right off the top of my head, I suspect that your accessory drive belt is either too loose or it is worn and 'glazed' and probably needs replacing.
Loose or glazed fan belt?
Brakes most likely
squealing or squeaking or a high pitched sound of discontent.
You need to lubricate and clean it.
iwhat does the noise sound like. most likely a worn belt or belt tensioner if its a high pitched squealing noise.
WD40 applied at appropriate places.
If you hear the squealing when applying the brakes, the pads are worn out and need replacing ASAP. Failure to replace the pads immediately will result in worn out rotors which will also need replacing. If the squealing noise is not when braking it may be a worn drive belt.
Water in the drums or on the pads.
the water is entering a moving part that it should not enter and or effect.. make sure your belt is tight and have a shop check your wheels if that's where the noise comes from
When it is time to change the brakes on your 2001 Mitsubishi Montero, they will make noises. There could be a grinding or squealing noise that you will hear.