I have a 6.1 engine. No mechanical noises but as the mileage has increased, the exhaust has gotten louder. I think it's because of the fiberglass in the resonators breaking down. The cause of this is water vapor, created by the exhaust, clinging to the fiberglass while the resonators are still hot. The fiberglass cools down with these water vapors and this repeated cycle causes wears the fiberglass and less noise absorption is the result. Rear Resonator with Fiberglass Packing Removed Fiberglass Packing Inside Resonator
You didn't say whether you like or dislike the louder exhaust Tom! One of my BMW's has gotten louder than the other which is ok with me so far.
