Only kidding! (I'm such a kidder)
Yes check to see if there is access to the crawl space and what you have for ventalation down there. You also need to check the soil. Sometimes, if there is dead soil, it will smell like rotten eggs.
You also said there is no access to the attic, make one! Again you need to check the ventalation there as well.
If all else fails, do a head count in the neighborhood!
Ps.. Servicemaster can get rid of almost any smell but it would be nice to find out where it is coming from.
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