I've been noticing that my 450 sx-f has a popping and backfire sound when i let off the throttle, happens a lot coming in quick to corners...the bike has less than 5 hours on it... carb is clean... i feel like its a jetting/ air screw issue, any information would be greatly appreciated!

Put some red-copper gasket maker on each of the exhaust joints, bad seals can lead to this along with being too lean.  My 08 250 done the same thing and with a jd jet kit and sealing the exhaust it stopped.