the reason you read about rattles so often (IMO) is many of the users here expect much more from the car... sometimes its because its the first new car they bought - other times its because its the most expensive car they bought…. Let’s not forget this is an entry level Infiniti = glorified Nissan. The G35 sedan will have no more (or less) rattles than any other comparably priced car.

Bottom line is these cars don’t have any more/uncommon rattles than most other cars. Acura is known for better fit & finish, as is Lexus - however, Infiniti isn’t a dump.
I've had my sedan for 4 years... it doesn’t have anything that I wouldn’t expect form any other car and nothing that is not tolerable or able to be fixed. In fact in 4 years there has only been 1 primarily (mild) rattle that I even took the time to address.

Drive the car you are considering and have a listen for yourself. If there are no rattles, get it. Basically same with any car.