Thanks for the information. Prior to getting your response I took a hand cloth folded it and placed it between the plastic base and leather on the left side of the front passenger seat. This stopped the rattling
noise. However, this is temporary and it doesn't look good but I have some temporary peace. I will take your advice about taking off the seat back (however, I am mechanically deficient, so I will be careful). If I can't figure it out I will take it to a certified MB mechanic.