Originally Posted by GoRomeo
Based on my experience...
If you get the squeak without pressing brake pedal, most likely are your rotor and pad lips or sliding pins not sliding well to open and close the caliper due to brake dust accomulated or lack of greese.
If you get the squeak when pressing the brake pedal most likely is due to worn out pads/sensors touching rotors.
Your not suppose to grease the pins, only clean them with brake cleaner, the grease will cause the rubber bushing to swell and cause them to start sticking, they are designed to work dry.
I been having the squeaking on accel problem for years, recently a BMW Tech told me to check the rotor backing plate, if you hit this often when you remove your wheels it could be rubbing the back of the rotor.
I'm planning on pulling my rotor off (passenger side) and checking this today.