My 2007 Cobalt always makes this strange noise about 10-20 seconds after I shut it off. It's hard to describe this noise but it sounds like something is purging back by the gas tank. The noise only lasts for a second or two. The car runs fine and the check engine light is not on. Is this noise normal?

 

does it sound like a knocking sound?

 

Yes, more so like a tapping noise.

 

thats normal i think its the evap venting?

 

Mine does it too, sounds like an empty spray paint can.

 

Roger is right its the evap venting and a normal sound no worries mate