Car has a loud tapping noise under the hood
First thing to do is check your oil. Pull the dipstick and make sure you haven't run it dry. If you have plenty of oil, do you hear a loud ticking like in the top part of the engine under the valve covers? If so, you may have a bad lifter. Check your belts. I have seen them split and slap against things when the car is running.
It could be a few things, like it could be an exhaust manifold that has developed a hole, when this happens it could sound very similar to a tapping sound, and maybe check the engine bay for anything that looks kinda loose that could attribute to the sound.
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