Dryer has a dank smell, which has recently

dryer has a dank smell, which has recently started.
The unit is basically very clean, nevertheless I have cleaned, washed, santized the drum many times, but the smell remains, although diminished. I am wondering if a belt is rubbing?.

I could not find an easy way into the unit to see - it seems as if you have to take off the sides and back as one unit?. How do I do that if necessary