I call this the "happy bees" smell.  I think it's as much pheromones of
some sort anything else.  I notice it around my hive, too.  It does seem
to have appeared when the bees were building queen cells, though.  I'd
check on this.  It also seems to be associated with a good honeyflow (which
would lead to colony buildup, which would lead to desires to swarm...).
 
Jane B.