i think there is something wrong with my x5 ... the first day i had the car the exhaust sounded loud ( growl...) i had it for 2 days, and then i noticed the exhaust sounded really weak ( just like lexus lx and mercedes ml ) and the next day i tried reviving it and the growl came back... and today it sounds really weak... can anyone please tell me why it is like this, and what should i do... does anyone have this problem?