I have recently bought a 2005 CLK320 Convertible which is pretty much faultless and I love it! However, when the engine is cold, it has a very growly, throaty sound, like inlet noise and almost like it had no air filters!. (it has!). As soon as it is up to operating temperature, the noise seems to go away and all is quiet. Is this normal? There seems no effect on starting or running but I thought it was just a bit odd. It is quite noticeable and I have had passengers comment too!

Any ideas??