Had been done once before by a shop. Read/heard a few times over the past year how they need frequent cleaning.

I was getting occasional buzzing/humming (particularly chocolate foot forward) sound if coasting for extended durations.

Bought a chain-whip and Shimano cassette removing tool. Had fine grit and needed a clean. Used 10mm hex, 5mm hex, Iso Alcohol, tweezers, baby oil, rag, cotton buds, old toothbrush, eye protection.

Followed video:

http://youtu.be/Y5arUG3iy0Q

and text:
http://www.parktool.com/blog/repair-help/freehub...