electronic whine sound when care is started in cold weather

Hi all, when I start the truck, for the first 15ish mins, it sounds like an electronic whine coming from somewhere in the back. How can I fix this or what is going on?

might be the rear air compressor

rogertheracer said:

might be the rear air compressor

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Per OP signature he has a Z71 , that model doesn't use an air compressor for the shocks. (only LTZ models).
Only thing electrical that could whine in rear is maybe the fuel pump? Or if you have aftermarket speakers. Other sources of whines could be the temperature sensor over drivers head in headliner or even navigation disc etc. in entertainment system.
Non electrical whine in rear could be things like rear diff or wheel bearings I guess?
Good luck finding the cause...

How cold is it when you start it? GM fuel pumps tend to whine when they?re getting ready to fail, or in extreme heat I found. Darn near pissed myself one year when I towed my boat out to the river, it was about 118 ambient temp and my pump was wining like crazy, I guess perhaps because the fuel was so warm. At 130k miles as soon as I got back I swapped the pump out for a Delphi unit and haven?t had an issue since. So i?m Not sure if it was due to the weather or it was possibly going out. Once it cooled down it didn?t make any noise though. While the vehicle is running go and put your hand on the fuel cap and see if you feel or hear any humming echoing through. I would say pull the cap but you?ll likely throw an evap code.