Quick question noise related.

I'm sure this is a stupid question, but. Shortly after starting my truck(11 TRD sport tow package) I hear what almost sounds like an air gun zip very brief. Usually after taking out of park. The truck is stock as far as I know I've had it about 1 1/2 months now and have heard this several times and I'm just wondering.

 

I know exactly what you are talking about my (11 TRD sport w/ tow package) does the same thing, I have 42k on it now and bought it brand new. It has done it ever since day 1......No answer to what it is though.

 

evap pump, thing located behind washer fluid bottle purging fuel vapor...very normal.

 

Cool, I didn't think it was a bad noise. Just always wondered.