The most obvious symptom of a faulty hydraulic lifter is the noise it creates in your car's engine. You can usually distinguish the faulty lifter by the distinct sound. Instead of a knock or ping, a faulty hydraulic lifter will usually make a sound more reminiscent of a tapping sound. The tapping will be quick in rhythm and may occur when the vehicle is cold or hot, depending on what the problem with the hydraulic lifter is. The lifter may be having problems with a sticking check valve, dirt, wear or other problems. It may be time to replace them if a oil change or flush doesnt resolve the issue.