Dead bodies stink. One reason is all the gas they produce as they break down. Loads of gasses build up and the body gets bloated. The thing is, that gas has to go somewhere which leads us to bloaters.
Zombies that move around are more likely to start popping that gas out whatever holes there are in their skin. And silly as it sounds it’s not at all unlikely that they would be shambling burping farting stink bags. Bodies that end up bloated have likely been sitting around for a while. Once they get up and start moving, the gasses start coming out and the stink could be unbearable. Best thing to do? Cover your face with a wet rag and dispatch that thing as soon as you can.