Buzzing is normally a sign of air in the fluid but that noise comes from the pump, not the gear box. GM typically has very little trouble with the gear boxes on their trucks but the pumps on their cars are known for becoming noisy. I'd recommend starting by having a mechanic listen to the sound to determine if it is indeed a buzzing related to air or if they think it is a symptom of something else.
In the '90s, Chrysler had some Dodge trucks that developed a buzzing noise in real cold weather, but only on the diesel engines. They came out with a special "cold weather" power steering fluid which cured the noise. I haven't heard of anything similar going on with the GM trucks, but it might be worth asking a GM mechanic.
There have also been service bulletins related to normal power steering noise being transmitted into the passenger compartment. The fix was a redesigned high pressure hose. Thinking along those lines, check the routing of your high pressure hose to be sure it isn't making contact with anything. Hissing from the movement of the hydraulic fluid is normal but it shouldn't transfer into the cab.
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Thursday, July 7th, 2011 AT 7:36 AM