I've got an 18 FXBB, 6500kms on it and still stock. I've noticed in the last month or so when I'm braking, usually slow speed to a stop, the front has started to make a weird groan (for want of a better word).

My front rotors made an unusual noise coming to a stop too.....turned out the rotors were warped. Not enough to cause shudder at first, but eventually at high speed, braking hard, a shudder developed. The dealer said the Torque specs for the rotor bolts were all uneven and they were replaced under warranty. Haven’t had an issue since. I’d take it into a dealer and have them check runout.