Volvo: noise when braking, brake job, highway speeds

Question
My 1992 240 makes a very loud, low-pitched humming noise (probably a vibration) when braking, especially after the car warms up. I recently had a brake job so I took it back. He redid the brakes and said he just couln't find what was making the noise. Can you shed any light on the subject. Thanks...

Answer
It sounds like you might have a warped rotor.  Try braking lightly at highway speeds, does the sound appear then too?  Sometimes the rotors can get misshappen, and require resurfacing.  I would have them removed and inspected for this problem.  Good luck!