When driving my 2015 Avalon it is making a tapping noise from under the engine. It has 18000 miles.
My car has 18000 miles.
My car has an automatic transmission.
The engine may be having a lower engine piston slap noise or the more common timing phasers on the camshafts. First thing to do is to make sure you are running the recommended oil for your engine. If you run too thick of oil will cause the camshaft timing phasers to not work correctly. If you are running the correct oil weight then if the vehicle is still under the basic warranty to take it in to the dealer before any internal engine damage occurs. I would recommend having a mechanic, such as one from YourMechanic, diagnose the cause of the noise and determine what repairs are needed.