Hi everyone, I can’t put a very long video of the sound but once I cold start my g37x, I get this really weird rattle sound coming from underneath my car which settles down after 15-30 seconds. The only time I hear it again is sometimes when I press the throttle I hear the rattle coming from underneath my car, I only hear it when the windows are down. I’ve already brought it to a mechanic and they walked around hitting stuff underneath the car and nothing was making that sound so I’m guess it’s something internal, but I’m not sure. My friends said it can be the catalytic converters or the resonators. My car is a 2012 with 129,300 km which is like 80,000 miles.

 

That’s just your cats warming up. Mine do the same. After one good rev it’s usually fully warmed.