I bought my new 2020 Silverado 2500 HD about 3 months ago and every time you open the door after it sits for a little while I hear this whoosh of air coming from the rear end that almost sounds like air bags decompressing. I’ve checked the truck has no air bags, I called my dealership they have no clue what I am even talking about. It’s not causing any issues that I’m aware of. Can anyone enlighten me as to what this could be? Thanks in advance

 

It's your fuel pump priming. It's a little odd it was designed that way but it was.