Hmm just so you know the impeller and water pump are two separate items although both circulate water to (impeller) or through (water pump) the engine.
Squealing could be caused by anything usually belts squeal if warn, glazed or not properly tensioned, sure you don't have an idler bearing that is going, maybe the bearings in the alternator or PS pump (these squeal and moan really bad if low on fluid).
Yes a water pump can make noise but usually if the bushings or bearings go bad there is evidence of a leak around the shaft and noise combined.
I've never heard an impeller squeal and furthermore if you start the engine and run it for as little as a few minutes dry you'll destroy the impeller as it is just a flexible rubber vane in a stainless steel housing. It needs water to lubricate itself, lack of water will destroy the rubber.
I'd do a little more troubleshooting before you start throwing parts at it.
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