Jojo, I haven't noticed an increase in noise while using bullpups. However, I try to use good hearing protection. Using a shotgun indoors is very loud, whether a conventional shotgun or a bullpup shotgun. Think about how short the barrels are on handguns or PDW's. I've used a suppressor on a Keltec KSG shotgun indoors, and the difference is amazing, but that's the whole idea of suppressors.
Chris, that was an outstanding outline regarding bullpups. I've had a KSG for a while now, and it's definitely my "go to" shotgun, because of its shell capacity, balance, and compact format. I recently acquired an AUG, and after using it, I'm impressed. I'm not a big fan of the AR platform, though I have several, AR's seem to be very utilitarian. The AUG is an elegant firearm, with nice lines. A spare parts kit is on order! But then again, I have spare parts for most of my firearms, just in case.