Smelly Washing Machine

This is a new one for me........

I have a top load machine, the kind with no agitator. It's about 4 yrs old.

I always leave the top open when not in use.

It has started to smell really funny...kind of like a funky musty/moldy type smell. It is coming directly from inside the tub. So far the clothes coming out have no oder.

Here is what I have tried so far.....
washing empty with really hot water and bleach
washing empty with borax
washing empty with vinegar and baking soda

Nothing has worked......please help!