Squeaking/squealing noise

I have a Mazda 3, 2008. The front/rear brake pads and rotors have been replaced/resurfaced. However, I still get a squeaking/squealing noise SOMETIMES. Ican’t figure out any pattern to when I get the noise. It happens morning, afternoon, after coming off the freeway, driving around locally. Any ideas?

Water is one thing that will cause squeaking brakes. Do they squeak all the time?

No. That’s what I can’t figure out. There seems to be no rhyme or reason as to when they do/don’t squeak. However, it was parked outside for a week, and it did seem to squeak more for awhile.