Due to that I heard the "keek" sound when I pushed the brake, I checked brake pad and pin in the brake caliper. Brake pads were OK but pin was little big dirty. I just cleaned up the pin and drove my car. However, there is still "keek.." sound. What is other possibilities of this sound? Thank you very much.

 

I get that sound sometimes when I flush my wheels with water.
It tends to go away very shortly after you drive it.
not sure if that's similar to what you are experiencing

 

Yeah, go and do a couple of hard stops and really get those brakes hot. that usually makes my squeaks go away.