Hello, my name is Steve I just got a 2005 c90 it feels great but I here a slight rapping noise when I first start to accelerate and if I’m going say 60, 65 mph. and give it just a little gas I hear it until I give it a little more gas. If I increase the throttle slightly and hold it, it will continue to make the rapping sound until I give it more. Do you think this is normal or possibly a motor problem? Thanks Steve.