Noise when braking, and it's not the pads
I had a quick question- Whenever I'm braking and I happen to drive over a bump in the road or anything, I hear a "RRRRRRR" noise. It's not a squeak or anything. It happens only when I'm coming to a stop and if there's some kind of obstruction in the road, when I drive over it while braking my car makes a kind of sounds that can only be described as "RRRRRRRRR" and the braking pedal seems to go in a bit deeper.
Is this normal? It doesn't seem like it would be. Has anyone else experienced this? I have a 2002 M3, around 45K miles. I don't think it's the brake pad, and am kind of stumped.
Thanks in advance.