panej

I hear a loud exhaust noise from the front when driving and get much louder when I drve through a puddle if it rains or snows. If the Truck is idling, it sounds fine but when driving you could hear it a block away.
Any clues?

DIYwannabe

The most common problem with the exhaust are cracks in the weld seams of the Catalytic converters. It seems to be a structurally weak point on the MLs and can cause a lot of grumbling from directly behind or under the engine compartment. You need to get under the truck when someone revs the engine and see if you can locate the noise. The exhaust goes something like this. Two manifolds from each side of the v-6, two precatylitic converters with O2 sensors before and after. Then comes the two catylitic converters, then the driver side exhaust path has a resonator, then both exhausts empty into one big muffler. I had a leak in my passenger side precatylitic converter which would have cost a fortune to replace. There has been alot of discussion about fixing the weld seams by re-welding. This worked for me, but there are other opinions out there. In my mind, it's worth a try if you can get a good welder to spot weld it for $20. Beats the hell out of a $2500 exhaust system! You may still have emmission/inspection issues to contend with.

Greg

PS:
other possibilities include:

Manifold gaskets (6 - one for each cylinder, or 8)
EGR Valve (SP?)
Air Pump

All of these are near the front of the car. Go to a trustworthy muffler shop and have them take a look at it, then decide how best to fix the problem.

panej

Took it to the dealer and the Cat converter was replaced under warranty since I'm still under 80000 miles but out of warranty.