So whenever my G37 is parked for awhile I'll turn it on and the exhaust makes some weird noise for the first few seconds the car turns on .. Does anyone have any idea on what this could be?

 

Welcome to the site!
The motor vibrates more at the low rpms at start up so it's likely your catalytic convertors' heat shields, it's fairly common.

 

Oh really man??? Thanks a lot I really appreciate it!!!

 

Welcome to the group. I'm also in Houston. My 13 G37 sedan does something similar. I have actually timed it and recorded the sound with my phone to email to my service manager. Mine will make the sounds when cold and clears up after 18 seconds. I think it is a combination of a lot of fuel being used during start-up (running rich) and the expansion of the exhaust system. On my car its the exhaust note that actually changes rather than loose or rattles from shields. My previous G35 did not have this noise upon startup.