Fuel Injector problems of the 2008 Toyota Highlander

Leased the car new. On the odometer it had over 60 miles registered. From the first day, the valves were sounding loudly. The valves are still sounding loudly, at 15, 000 miles. I informed the service dept, but really nothing was done. When warming up the car, when I first had it, the car was running very rough. The service dept. Corrected this. At 15,000 miles a fuel injector had to be replaced. Service consultant states he will check this in one year. I wanted to know how come the fuel injector had to be replace and was this normal in other car. New fuel injector was inserted. Old part is not available.