2001 E430 Exhaust Rattle?
 

2001 E430
94,xxx miles

Upon arriving home from work last night I noticed a rattle that sounded like a loose heat shield, however, I cannot determine whether it is in the front, near the transmission or the back, near the muffler. Seems the exhaust (or drive train?) is rattling in some way.

It occurs most noticeably in idle/park at low rpms; and when I was braking to turn into a parking space. Revving tends to quiet it.

My assumption is a loose heat shield or exhaust hangar. Any other thoughts?

If you can get under the car you might use a rubber mallet to check the cats. If they make a noise they could be failing. Failure is usually caused by a faulty MAF allowing a too rich mixture and overheating of the cat.

That seems to be the case -- with one of the secondary cats in the middle of the car. The two forward ones with the O2 sensors are fine.

Because the secondaries are not regulated, the tech suggested cutting them out and replacing with just pipe, which he said would improve my fuel economy and performance. (Over the past year I have indeed been using more fuel and the car seems a bit slower on acceleration).

I asked about back-pressure issues and he said the resonator and rear muffler provide most of that.

I will likely follow his suggestion or at least weld in an aftermarket Magnaflow in place of the broken cat. Has anyone else done this?