Why is the ford fusion hybrid engine making noise?

Noises coming from the engine of the Ford Fusion Hybrid such as knocking can be related to using the wrong type of fuel (too low of an octane rating), a failing or broken timing chain, or a clog in the air filter. If You are hearing a clicking noise, that may mean an issue with either the valves or valve lifters. Hissing noises are often due to a leak in one of Your vacuum hoses or a problem with the cooling system. Noises that seem to be coming from other areas around the engine could be caused by a failing water pump, A/C compressor, or the power steering pump. If the car is having issues at startup there could be a clog in the fuel filter or catalytic converter or the spark plugs and wires.