Hi

I have had my 7 year old C Class Coupe for 6 months now and love it.
The only problem I have is that recently it has developed what can only be described as a dry tapping noise that increases in tempo the faster the car goes. It increases the more pressure applied to the gas and vice versa, but it never happens when the car is stationery not matter how hard I rev it.
I have taken the car to my local Merc specialist and they found nothing, but still charged look at it.
Any ideas as I'm sure its getting louder.

Many thanks