One of the most aggravating noises (ka-ching!) for a driver is the metal-to-metal scraping or grinding sound of an automatic transmission that's low on oil. You should immediately check transmission fluid levels, and if low, add fluid which should correct the trouble.
If the noise persists, the problem may be a clogged transmission filter, preventing fluid from reaching the pump. With the proper amount and pressure of transmission fluid, the transmission's pump and other components will quickly fail, leading to a very large repair bill.
To prevent this scenario from happening, the automatic transmission fluid should be checked regularly (about every time you change your oil), and the fluid and filter are replaced periodically.
You should ideally check fluid after the vehicle has been driven a few miles amd the engine and transmission have reached normal operating temperature. It should be either pink or red, but if the fluid has turned brown, this indicates it has been burned (and it will also smell burned). Burned fluid should be drained and replaced, as should with the filter.
The tip of the dip stick should be cool enough to touch; with an automatic transmission operate at 65-95 degrees Celsius (150-200degres.F). hard driving which can overheat the transmission, may suggest the installation of a transmission cooler, which would significantly extend transmission fluid life.
If you are driving your vehicle hard, then you should have from frequent fluid and filter changes than the Owner's Manual recommends. This would include: