2002 Mercedes Benz S430

Brakes problem
2002 Mercedes Benz S430 V8 Two Wheel Drive Automatic 92000 miles

My S430 has had some issues lately. There is a rattling noise that began about a month ago that seems to come from under the right side of the car. I thought it may have been a pipe rattle. But, I was driving in my neighborhood and the car seemed to lose powe, r similar to a loss of compression. The mild rattle became extremely loud, almost like dragging metal. The trouble light came on " BRAKE CHARGE TAKE TO GARAGE" and stayed on until I got home. After about a minute, the trouble light turned off and car was idling, with the noise quieter. I stopped the engine and started it again. It did start. I did check my battery and there was some moisture near the posts (a paper was wet that was on the battery in the trunk). Could this all relate to a battery issue? A catalytic converter? She has been hard starting a little recently, too. Thanks for your help!
August 10, 2010.

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