New exhaust - now have backfire

[PHOENIX]

I put on new headers, new y-pipe, new cat and new muffler (aero chamber).
From y-pipe back its a single 3" pipe all the way out. Cat is in stock location, muffler is about 1'-6" in front of rear axle, pipe goes over rear axle and out behind drivers tire like stock.

When I rev it up like 3000 rpm + and let off the throttle there is a few back fires right before it returns to idle speed. What causes this?
Is this carb settings, timing issue or is this what I should expect with this higher flowing exhaust setup?

I will try to get a video or sound clip up later to show you what I am talking about.

Thanks!