2T/Gas Gas Newbie Question

[phoenix]

I have only ridden four strokes and my 2013 Gas Gas 300 is my first foray into the two stroke world. With that being said, there is a noise that comes from the bike that makes me curious. It sounds like when you open your throttle and let it slap shut...like the slide on the carb whacking shut. It happens when I'm on the gas, though, not necessarily when I close the throttle. I'm sure you're all snickering because its something obvious, but can anyone enlighten this 2T newbike as to what the noise is (and is it something to worry about)?