"All this was done by me three years ago so I'm a bit reluctant to assume all that is ready to be replaced. I used all OEM parts and some MB if I'm remembering correctly."

All this was done by me four weeks ago and the new alternator died, dead as a hammer, no output. That's why I'm getting rid of mine. Tiredof working on it once a month. Take the belt loose and see if you can spin each individual component to see if you have a bearing going bad. If not, it's a bad belt or a bad tensioner.