Family Guy

My Mother has a 1999 clk430, see just had a major service done and her warrenty is up. This morning see drove me to the airport and when she started the car it had a knocking sound then as the car warmed up it went away, as I was driving, I heard a slight clicking noise, it was very cold this morning in New York. Does anyone have any idea what this might be. Thanks in advance for your help.

C23K

Sorry, I'm the farthest thing there is from a mechanic. Although if you post this in the CLK forum I'm sure you'll get a lot more responses