I recently had a rattle coming from the same area. Found that the front passenger side mud flap was loose. Give it a shot!

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Scott
2002 G500
2003 Audi Allroad
1999 Range Rover
1992 500SL (sold)
1999 ML320 (sold)
1989 300SE (sold)
1987 560SL (sold)
1986 300E (sold)
1983 300SD (sold)
1982 300D Turbo (sold)
1980 300D (sold)
1973 450SL (sold)