Screeching sound from brakes?

[shashankmittal]

I am noticing since a week that when I apply brakes and the car comes to a dead stop, the brakes produce a loud screeching sound. This happens only in rainy weather or after I wash my car. The sounds goes away once the weather is dry. Braking while driving to slow the car, does not produce this sound, its only when the car stops completely.

I researched a little and found that it could be a problem with the rotor or the brake pads. I have driven my car for about 20000miles. Does anyone know if it is time for me to replace the pads and/or rotors? Could it be due to something else? I just put on after market wheels and spacers on my car and I am not sure if that could result in this sound or is it just a coincidence.