My 98 E320 has a rattling noise noticeable only when I slow down while braking

The noise could be anything but what comes to mind. Catalytic converter going bad or something in the exhaust system loose Something in the front end loose without lifting it up It's really hard to tell

A sound like this drove me crazy for years. Dealership service inspection: "could not reproduce sound." Various other mechanics could not identify it or correct it. It was a subtle rumble coming from the front end when driving over uneven roads, such as those that had been repaired or new utility service patches in the asphalt were made. I even made test drives with the service managers of a few shops and and for the non owner it was hard to identify. Maybe it was slightly more detectable when holding the steering wheel. Anyhow, I requested that they put the car up and really pull on the front end components to see it there was any play in there. Sure enough, they found play in the stabilizer bars. They replaced the "stabilizer bar links" and that annoying sound has been gone for a year now. Sound started around 120k miles and links replaced at 150k. E320, 1998, sedan, W210.