Well Tracy,without any further description of the odor I can only guess that your attic smells like everyone elses...like a hot and dry basement!I'm sure you've detected that each home has it's own particular scent since we all have different lifestyles,furniture,cleaning products,carpeting,etc.etc.All attics on the otherhand,quite often are unfinished and are made up of wood,insulation,wires,and boxes of who knows what.This is one part of the house not usually heated nor occupied and temperatures can easily swing low to high throughout the year.Since attics rarely get a good vacumming they are also dusty as you mentioned.
I too have an attic fan but must confess I have attic odor as well.If I understand your layout,you can walk into yours.I need to acess mine by way of a 4'step ladder which normally is only at Christmas time.I associate my smelly attic with Christmas.Anyway,if you're trying to freshen it up a bit,you could try cedar shavings,moth balls or something else with a different odor.Good Luck!

"...a strange smell..." is kind of hard to get a handle on.