One problem related to loud engine noise has been reported for the 2008 Mazda CX9. The most recently reported issues are listed below.
When starting the vehicle there is a loud sound coming from the engine for 2-3 seconds . It doesn't happen all the time, but it sounds like a card going through bicycle spokes and is accompanied by a high rev sound . This sound also happens randomly when driving . It happens directly after the vehicle automatically shifts into a new gear, and is accompanied by a loss of power until the rev sound and card in spokes sound goes away. The power of the vehicle is normal until it makes that sound.