Yup, mine too. I was actually going to make a post tonight asking if anyone else's did it or not.

A few times a week when my car is cold and I first start it up, if I rev it will pop pretty good once or twice, it sounds like a small backfire.

 

Mine does that with the stock tune...no work here...just corsa's....
Only the start up....btw 1st and 2nd...thought I had a leak but no...all good.

But to be honest, was fouling around with my exhaust after taking the hitch off...and now that I think about it its gone..

maybe a slight ehaust leak.