Well if its a "musty" smell then you may want use anti-sweating stuff. I use "shower to shower powder." But if you have what they call...(and dont be offended)..."Swamp Ass". Then sometimes a simple solution such as a saline enema might help. Sometimes I get this smell when working out and sweating profusely. Sweat during these instances, will collect between your cheeks and under your sack and stay there unless cleaned out thru showering. A item I sometime use is a product called "Freshends" (its basically natural used stuff into a wet wipe nap..no it wont burn)Using that after doing number 2 or after hard super sweating activities might help lesson bacterial smells within those areas.
Unless of course these same people are trying to mess with your head.