Mine did the exact same thing. Check the tone rings on the back side of the rotors. If there is road grime and grease caught in the teeth, it may interfere with the ABS sensor voltage induction at slow speeds, fooling the ABS module into thinking there is a skid, when there really is not, and therefore opens the pressure dump valve and pulses the modulated apply valve and pump motor for the affected wheel brake(s) to regain traction.This explains the funky pedal feel. Tone rings first - Clean 'em. If this does not solve it, do what I did - pull the relay for the ABS ECU and voila - problem solved!
Your hard pedal is more than likely a separate concern. A vacuum leak or weak vacuum pump would cause this. I have thought about mounting a vacuum gauge next to my boost gauge for this very reason. I put the boost gauge in the glove box, angled so the driver can see. This way, I retain the stock MB interior with a tucked away subtle goody. I rigged the gauge light to the glove box light switch, so it goes on when the switch is tripped after the glove box door is open.