Some 2010-2015 Mazda CX-9 vehicles may exhibit an unusual rattle/buzzing noise from the pre-silencer when driving at about 1,800 rpm
The lower (rear-side) of the pre-silencer may be thermally deformed due to insufficient rigidity (fewer weld spots). The deformed portion may resonate exhaust gas pulsations, causing the noise.
A reinforced plate has been added to the pre-silencer to increase rigidity. Replace the pre-silencer part number (P/N) CA11-40-300C, along with gaskets AJ17-40-305 and FSB8-40-305.