A: When your car's brake pads are worn down, the wear indicators hit the rotor, causing a high-pitched squealing noise. That sound is there to alert you that you need new brake pads immediately. If your car is making a high-pitched squeal, make an appointment at your dealership's service department right away.
A: Unfortunately there are a number of problems that meet this criteria, ranging from air in the braking system to complete brake failure. It's best to have a professional look over the braking system and determine what the problem is. Attempting to do so yourself could cause damage to a major component and possibly cause an expensive repair, to say the least. You can find a certified technician at dealership service departments.
A: To really know what's going on with your braking system, a service technician would need to inspect them. A grinding or groaning noise, especially at low speeds, is normal for vehicles with semi-metallic brake pads and most front-wheel drive cars. The noise itself is just the vibration of the brake pads as they vibrate against the rotor. The noise is usually unavoidable but if it happens every time you stop, have a certified technician inspect it right away.
A: That's an incredibly complicated question that varies vehicle to vehicle. The only way to know for sure is to take the entire braking system apart and inspect each and every part. A complete brake job is rarely required to fix a problem, and most systems can be fixed by replacing a part or two.