I just installed new brake rotors and pads on the front of 2009 f150 and there is squeaking noise coming from the left front. Any idea on what it could be.

 

As I recall, your vintage F-150 is one of only a few vehicles on the road to have specific inner and outer front brake pads. If you install then incorrectly, you will end up with a noise. Other things to check include sticking calipers and bent dust shield / backing plates.

 

Throw some brake grease on the inner shim plates.