Help Identifying Part - Missing Part and Vibration Noise from Rear

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(I am trying to Identify the part below..)

Hi, I have more and more vibration noise comming from the rear of the car, always when RPM match 1000 or 2000, and engine is working. This guided me to a loose part around the muffler.

I jacked the car today and give a look under it, to find a missing bracket on the Catalyser on the Left Side. It is a Porsche Boxster 99







I searched in my Bentley Service Manual and I din't really found what that bracket was and where is it going. Can someone help me to Identify the missing part ? thanks