Loud hum or whine

I need help figuring out what this sound would be from. I have a 2003 Silverado 1500 4x4.
I get this high pitch whine from the front left side of the truck. It
does not matter if I am turning, braking or just moving. It does not last long and comes and goes.
At first I thought it might have been my tires, so I bought new ones. The problem still comes and goes. Then I thought it could be the bearings, but when I figured out you had to buy the whole hub to get the bearings, at $198 a piece, I dont want to replace it yet.
I have 57,000 miles on the truck that I bought used almost a year ago.
Please help the noise is driving me nuts! If you can suggest trying anything I would be most grateful.
Thanks,
Jason
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OhioChevy wrote:

A stuck or worn left front brake pad.......
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Power steering pump
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