What can this issue be? on 2004 Mercedes-Benz C240 4MATIC

At first It started with clicking noise from vents when heater or air was turned on. Now all of a sudden without warning a loud knocking from under the hood.

by in Charlotte, NC on March 06, 2013
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1 answer
ANSWER by , March 06, 2013
check your fluids. if you have low coolant or oil that could be your engine knocking.