Brake squeal can be a few things. If you're nearing the useful end of the brake pad life, it should have a metal tang that sticks into the brake rotor and when you apply the brakes it'll make contact, rub/vibrate and you'll hear a squeal. But you'd be hearing the squeal all the time, not just when it's hot or cold. I have had noisy brakes in many cars, many times it's just brake dust and crud that gets in there and fouls things up, either way, you need to take off the wheels and take a physical look at the brakes, check for worn/loose parts, check the pad thickness, etc. You might also have really bad brake rotors as well as bad pads. Just clean it up first with some brake parts cleaner, make sure you don't inhale any of the dust, it's dangerous for your health. I literally have had cars with noisy brakes and when I check I can't find anything, so I chalk it up to the parts, just change out the rotors and pads, those parts are super cheap on most cars, I personally prefer semi-metallic brake pads (if you can still find them) vs. the ceramic, the ceramic are very quiet and don't make a lot of dust but I find the semi-metallics have much better braking power, which, considering how I drive, I need all the braking power I can get, so I don't mess with ceramics if I can find a semi-metallic pad for the application.