When I turn my heat on it makes a short noise like its passing gas, what could this be. My truck is still under warranty

 

mine does it too.

 

Is it like a high pitched whine for a second?

 

hmmm it may be high just for a sec but mine will do it off and on all the time. Sometimes when it starts up there is a thud in the floorboard passenger side. It's hard to describe but I really don't believe its the blower... but it might be? Now that I think about it, I can really hear it when it starts up with the ac on.
When I switch the vents I can hear that thing moving. It sounds normal to me.

 

I don't know anything about the system or how it works but I hear they are not fun at all to work on.

 

Oh I gotcha, yeah mine only makes the whine for a quick second, but I haven't had any issues *knock on wood*

 

it is the blend door there is a TSB out for it, mine did it had it fixed under warranty. If your still under warranty just take it in and have the dealer do it, If not i heard it an easy enough fix to DIY.