Two problems related to loud engine noise have been reported for the 2005 Chrysler 300C. The most recently reported issues are listed below.
My wife was taking our two kids to school when the car made a horrible noise when first trying to start the car early in the morning. I had it towed to my mechanic where he found that the cylinder valve seat fell off the cylinder head and fell down into the piston causing severe damage to the valves and piston. Replacing the engine for $8000 was an option, however you are replacing it with the same type of engine that could potentially replicate the problem again. After researching this seems to be a manufactures defect of this engine for 2005-2006 Chrysler 300 c. This happened 4 months after my warranty expired.
The contact owns a 2005 Chrysler 300c. While driving at approximately 45 mph, the check engine warning light illuminated. The vehicle was taken to an independent mechanic but was not diagnosed or repaired. In addition, the contact stated that there was an abnormal noise coming from the rear passenger side wheel of the vehicle. The vehicle was not diagnosed or repaired. The manufacturer was not notified of the failure. The failure mileage was 73,000.