Visual/Physical Inspection

WARNING: This page is about a different car, the 2010 Chevrolet Aveo. However, it is still accessible from the selected car via links, so may be relevant.

Inspect for aftermarket devices which could affect the operation of the Engine. Refer to Checking Aftermarket Accessories .
Inspect the easily accessible or visible system components for obvious damage or conditions which could cause the symptom.
Check for the correct oil level, proper oil viscosity, and correct filter application.
Verify the exact operating conditions under which the concern exists. Note factors such as engine RPM, ambient temperature, engine temperature, amount of engine warm-up time, and other specifics.
Compare the engine sounds, if applicable, to a known good engine and make sure you are not trying to correct a normal condition.