@N-Raged just in case you're doing it wrong (which is the case sometimes).
If you want to test it properly, go for a drive and let your engine warm up properly, water and oil temperature should be at ~90 C for both before you give her hell. Go somewhere where you won't disturb others, and park it. Put it in N mode, and put your foot down on the throttle. Not gradually, all at once and at about 5k rpm pull your foot away, again, aggressively. It should bang, almost every time you do that. Mine doesn't do that always as well, and not always at 4k, and this is normal.
At first when I got the car I thought that it is quieter and doesn't bang and so on, but you really need to be aggressive on the throttle. I can drive all day long changing gears at 5k rpm without a single bang if I drive smoothly pushing gradually the throttle etc..
The same concept goes not only for neutral when you're stationary but for all gears. My advice is not to redline first gear or even more than 4k, not healthy. If you are on full throttle for example in 3rd gear at 6k rpm, go off the throttle, that should go bang bang bang every time. Whatever gear you're in, when you downshift and it goes above 4.5k rpm it should bang, but like I said, sometimes mine doesn't as well, nor did the demo I drove months ago. I found too that at higher rpms the bangs can be louder or more. If it still won't.. then like others said, get it looked at.