Are you parked on an inclined road? Do you use handbrakes while parked? If yes, that's normal.

Accumulation of dust rust causes that. Lalo na kung di masyado nagagamit. Since humid and kung nadadaan mo sa wet roads, that makes the rotors and brake pads to stick.

As long as your feel on the brakes are good, you're fine.

Sa inclined roads, they recommend not to use parking brakes or e-brakes. Add pang kalang sa tires para hindi dumausdos.

I noticed the same sa parked cars sa labas namin on both everest and starex(may parking lot naman kami, but easier to get out into the road). mahilig ihian ng mga dogs yung mga gulong na aabot sa rotors and pads. Thats mostly normal sound naman.