He probably means rear subframe bushings. They can be easily inspected and I would do so before replacing them. What do you mean by upgrade? The sportline bushings? I think the normal ones are fine, BTW there is not 16V for this engine.
Loose / worn struts could also lead to such noise, as well as shot suspension links etc. There is lot of stuff that can cause noise in the rear end. Good luck, Bruno

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300TE 1992 137'000 miles