My friend's E320 cdi developed a noise from the front suspension. It turned out to be a worn bushing at the bottom of the shock absorber. The cure - remove bushing, separate rubber bushing from metal insert, lag insert with insulation tape, hammer insert back into bushing, re-assemble and refit shock. Result- no noise. Cost-5p. No insulation tape, then use a cutting from a plastic bottle. Life of repair = indefinite ( last repair of this nature on a different car is still good after 30000 miles)