Guys so got a 2013 3.5 M sport with just under 7k. Since I bought it haven't driven much but have noticed when ever I do and start it up, the first few seconds there is a metallic rattle like two metal lids hitting. If I start driving away instantly and floor it or apply any gas it kind of get louder and then goes away. A friend of mine with an 08 4.8 had the same issue at about 45k. Any thoughts? I don't feel like taking it in yet but