Interesting...my wagon has the same issue. I have begun noticing a rattling noise in the morning when the car is in gear. I knew the catalytic converter might be loosing life (114,000 miles), and recently my LHD wagon has developed the ticking sound at 2000 RPM above (almost inside) the passenger side glove compartment. Thanks for the information. It looks like the cat is on its way out.

Are there any consequences to driving with a bad converter. I have noticed slightly sluggish throttle response, but is the engine being damaged?

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1982 300D-T (sold)
1988 300E (sold)
1994 E320 Wagon (sold)
1995 E320
1998 E300D-T
1999 E3204M Wagon
2001 E320
2005 E320 CDI