popping/bang noise under bonnet
 

my mazda 3,2004.always makes a bang or pop noise within a about 10 to 20 seconds after starting & pulling away.the noise is coming from under the bonnet.does anyone have any idea what it is.just annoying

If it's a very quiet sound, it could be the ABS system initialization. I know my mom's Nissans all make a noise when you get to like 3mph the first time after starting it.

--but I've never used Mazda ABS so I dunno