My case stunk too-- so much so that it couldn't be brought into the house and the stink got on the machine, as well. I tried the OdorEaters but they didn't quite do it. I ended up wiping down the inside of the case with diluted bleach, then leaving it open in the sunshine. It smells much better now.
I read that a fungus (mildew?) grows in the glue in the lining of the box. I think the horse glue breaking down is a better rationale. Whatever the cause, it's awful and you don't want it!