Smell coming from insie washing machine

This is usually caused by mostly using low temperature washes. The detergent manufacurers don't tell you, but low temperatures don't kill the bacteria present on most clothes, so they breed and and multiply in nice warm moist washing mashines. The cure is to do a "maintenance wash" every so often, which is the hottest wash the machine can do, and this will kill the bacteria. Also adding washing soda to this wash will help to freshen it up.