If it's new, just take it back to the dealer. But to do a quick check, with a tank connected and the tank valve CLOSED (best option) or the dust cap snuggly installed, put the second stage in your mouth and gently inhale. It should pull a vaccum and you should not feel any air entering the reg. If you do, determine where it's coming in from. Possible places are a bad diaphram, bad exhaust valve, defective mouthpiece or loose/missing wire tie, cracked case, loose cover or plug or any one of several Orings could be bad/missing. Unless it's a loose cover or mouthpiece issue which are easy fixes, it's under warranty anyway, let the shop fix it.