TM G36c semi auto problem

[Ghost Snake]

Just got a TM G36C a short while ago. Having some problems though. Full auto works great, but semi is messing up sometimes. Most of the time it works great, but every once in a while I pull the trigger, but nothing happens. No motion, no sound, nothing, dead. The only way to make it work again is to put it into full auto, fire a few rounds, and then go back to semi. This happens about once every 15 rounds or so. Any ideas would be greatly appreciated.