oooh oooh that smell! can you smell that smell?

we moved back into our renovated house two years ago. and for two years i have dealt with a nuisance that i have complained about. sometimes feeling pretty helpless because NO ONE WILL LISTEN TO ME! there is a smell. it is in the "added on" section of the house. in the boys rooms. JUST in the boys rooms. a PUNGENT rotten egg/skunky smell that only comes out when the "conditions are just right. usually late afternoon when it is warm outside. i have told paul the builder about it and he has not smelled it yet UNTIL YESTERDAY. i called him "come over NOW! skunky smell is back!" see, for two years i have blamed this on the paint. thinking we got a bad batch. but now, i am beginning to wonder if we got some of that defective dry wall that has been recalled! ugggggggggg! ok...so paul the builder comes over and HONEY, he smelled it and believes me now! peeeeeeeyew! what are we going to do? it HAS to be the walls. although paul got all of our sheet rock at the same time from the same place and the boys rooms are the only one that seem to be affected. it is extra embarrassing when friends come over in the late afternoon and i have to just tell them WE KNOW that there is a smell, no one died under the house, there is not an archaic diaper that is fermenting under someones bed. so, we just close the door, until someone opens it to see the addition and it hits them like a skunky toot. oops, sorry. brett would rather me not mention it but i am in the school of thought that you want people to know that YOU SMELL THE SMELL TOO! "i don't want anyone to think wow do they know that their house smells skunky?" or "did they boil some eggs before we came over?" mmmmmmm rotten eggs......