Sounds like the fan bearing to me.

You probably need a new fan and fan bearing. When mine went, my friendly and trusted MB man in Wimbledon fixed those items and installed a few new 'jocky wheels' too and all's been fine ever since.

The noise struck as we were motoring towards London in the Loire valley. We managed the journey to London with ghastly noises but, mercifully, nothing broke.

Best to get it fixed soon, sooner, soonest as disintegration could cause untold damage.

The best to you.

RayH