I have an '03 Toyota 4Runner. Replaced front brakes 2 years ago because they were squealing when I applied brakes. Was told they would continue to squeak until they were completely broken in. They continue to squeak when I apply the brakes to this day. But only at light pressure. Once I push harder on brakes, the noise stops. Also, now a NEW squealing noise has started and getting progressively worse. Different because it squeals when I'm driving, and stops once I apply the brakes. But then the other noise kicks in that's been there since before I had the front brakes replaced 2 yrs ago! This new squeaky noise happens in reverse or drive, and the noise accelerates and decelerates with the car, depending on how fast I'm going. It's loud enough that people look to see what's making the noise. HELP!
There are a lot of things professionals can do to prevent brake noises. Some of them only apply to the break-in period. If the squealing can be prevented DURING that break-in period, the pads are less likely to squeal during the rest of their life. I have a whole list of things to do and not do when it comes to noises but it is mainly useful to do-it-yourselfers.
There are other causes of squeals that should be investigated. One is a front axle seal. When worn, the rubber sticks to the rotating axle shaft. That is best heard in a parking lot. Flooding the area with a spray-type grease until it finds its way to the seal will stop the noise from anywhere from an hour to a few days.
When the brake pads wear down far enough, most have wear indicators that screech lightly against the rotors. Sometimes they make noise when the brakes are applied, but more often when the brakes are released the pads can twist just enough to let the indicator make noise. It's very common for them to be quiet when braking.
The place to start is with a brake inspection. Sometimes a tool called a "Chassis Ear" can be helpful. That is a set of six microphones, a switch box, and headphones. You place the microphones near suspect points, then listen while driving. By moving the microphones around you can zero in on the source of the noise. Be aware that many mechanics have never heard of or seen this tool. Most new car dealerships have them.