How do I get rid of this odor?

I have a Nissan stainless steel coffee mug which is about 5 years old. I have used the heck out of it, but now the inside has a permanent (?) odor. I have tried hot soapy water, and the dishwasher. The only thing I have NOT tried is bleach - any ideas??? Baking soda perhaps? This mug is indestructible and I don't want to have to replace it. The inside is completely stainless steel , no plastic of any kind. Thanks in advance!