How certain are you that it's not the ignitor firing for some reason? You
said you looked at the flame and didn't see anything in time with the snaps
but you wouldn't if it was the ignitor. I'd light a burner then kill power
and see if it still does it. If so then maybe it's some odd thermal
expansion thing which you'll have to track down by listening closely to
where it's coming from. But eliminate the ignitor first.