If they just started free ranging, I would say its just free range eggs. If they have been free ranging, but the taste just changed, I would say they have found a new food source such as the onions mentioned or something else.
Yep, I'd agree. You're just not used to the more "eggy" taste of free-range birds. They could be eating some onions or something though. Usually they won't eat smelly stuff like that anyway. If you are giving them flax seed, that can give the eggs a strong taste. Also, make sure you are not storing your eggs near something stinky in the fridge, as this can cause them to absorb stinky flavors. In the wintertime when it is cold, I just store mine out on our enclosed porch until freezing weather, then I put them in a cool place in our house. Then they don't have the chance to be stored near any strong odors (we don't have a fridge).
The thing is they have been free ranging all along. The eggs were fine until the last couple of weeks. I only supply nutrena layer feed, grit, and oyster shell. The only difference is I used to let them out to free range all day, and now I don't let them out until the afternoon. The reason for that is some of them were laying in the yard. Now I wait until after they are done laying. Other than that everything is the same.