When i turn my stove on its the same story for a few seconds. My guess is that it is the natural gas that is released in the seconds before the flame turns on. If it is a constant oder then you have a problem!
It happened last week on Thursday then again today
Does it smell somewhat like rotting eggs? If it smells the whole time your cooking your stove may not be burning all the gas its supposed to in which case you need to inform your gas provider. Breathing in those fumes are harmful