Good fresh powder will have an ether-like smell. I tell folks that if your powder smells lke a hospital, it's still good.
However, your situation is with already loaded rounds. Since you say you don't have the smell when factory ammo is stored in the same cans (true?), but you do when reloads are stored, it sounds like its not the can and there is an air leak with your reloads. This can be loose primer pockets, crimps that aren't tight enough, or at worst, you could have a split case somewhere in the batch. I wouldn't worry too much about it (unless its a split). But remember, if there is a leak where the powder odors can get out of the case, then things can also get in.