One problem related to loud engine noise has been reported for the 2009 Ford Flex. The most recently reported issues are listed below. Please also check out the statistics and reliability analysis of the 2009 Ford Flex based on all problems reported for the 2009 Flex.
July 22, 2016. Wife started car in school parking lot and headed to the exit. While making a left hand turn onto the main road, and accelerating, loud noises again heard under the car and it lost power even while giving it gas. Had to pull over to the side of the road. Shut off car and re-started. No issues. Wife refuses to drive the car until fixed. Taken to dealer on July 29, 2016. Unable to duplicate. Returning to dealer Aug 5 for computer re-flash. This is a significant safety issue that is being reported all over the Ford Flex forums and it appears Ford motor company will not address the issue.