For some reason it is usually the scrolling down that gets sticky on my MM. confused Sometimes it chatters as if there were a slipping gear inside.

I have sometimes found the build up of body oils and dust in the scroll ball needs a bit stronger cleaning solution than that recommended by Apple. Placing a household cleaning wipe on a semi-soft surface, like a soft mousepad and then turning the MM upside down and thoroughly scrubbing the ball across the cleaning wipe in every possible direction several times has always cleared it for me. Good luck!

If we knew what it was we were doing, it wouldn't be called research, would it?

— Albert Einstein