When I turn the steering wheel while driving I get a squealing sound . It appears to be coming from under the hood , gets worse when it rains .
Squealing is the drive belt for your power steering pump. You probably need a new belt, but the pulleys and tensioner, if there is one, should be inspected as well. Make sure the pump turns over freely when you have the belt off. Check the power steering fluid; if the reservoir is empty and the pump feels seized up, you may hhave an expensive problem on your hands with a failed pump.
The belt that drives your power steering pump, and possibly other things, is loose and worn.
Have a new belt installed and properly tensioned and the noise will go away.
removed old belt checked tensioner and all pulley’s installed new belt,noise still persists
Since you’ve changed the belt and checked the tensioner, the only other likely candidate is the pump itself. If the pump bearing is binding it’ll load down the belt more than normal when you engage it and will squeal.
With your head under the hood, have someone turn the wheel while the engine is running. If you’re uncertain where the squeal is coming from, try touching the pump with a metal rod or screwdriver and touching the pump housing. If that’s the source the vibrations will com eup the rod. Do this carefully, so as not to get caught in something spinning.
Note: if when the car is steered you see the belt wobble, that’s a good sign that the pump is loading the belt too much.