B-Pillar rattle

I have a 1999 MB C-230 and for about 5 years have had a slight, but noticeable rattling noise in the driver’s side B-Pillar probably caused by a loose cable or wire that shakes when driving over irregular surfaces - country roads, in particular.

Any suggestions for getting in there and fastening the culprit?

The factory body manual will show how to gain access if possible, otherwise maybe shoot some expanding foam in there.

The interior trim on the center post needs to come off. It normally snaps on and off.