why a fcar sound louder if you dont started a longer time

the oder day my 360 spider had a much louder start up like 3 times louder than the normal start up sound that it makes when you leave the car 6 or 7 days off.
also in the hi way it sounded diferent and louder, and when i parked the car for 15 min and started up again it was also much louder than normal.
can somebody tell me exactly how that works.
i know that the car sounds louder if you start it 2 or 3 hours later than if you start it in 30 min,but in the 430 it sounds like always the same.
i know that the valve open quickly when you start up but yes i dont understund the life of the exhaust.