i own a 07c230 sport with about 27000 miles on it at first the dealer said it was a spark knock so changed fuel but i use premiun anyway so i changed gas station jhust in case but it was still there so i took it back and now the dealer say it was normal before the noise is coming from the intake. they say the noise is when the intake runners are switching from the short runners to the long runners. and this is suppose to be normal. the noise its must sound like a spark knock cause at first he said that was the problem any body out there heard of this or owns a c230 with the 2.5 v6 thats hearing the same noise??????