Best thing you can do is check the pads for glazing,and keep the pistons cleaned up with brake cleaner..

 

My 2012 FB has done it from day 1. I brought it back to the dealer and was told it's normal. It seems louder when breaking down from 50 to 30 mph. Below 30 I don't hear it at all.

 

8,000 miles and still does it. I just figured it was the pads. No problem.

 

It's the cooling holes in the disc as they pass through the pads, it's normal and unfixable period.

 

Also the disc is a floating disc, another sound you will hear is, example; you roll it back, apply front brake, then take off forward, you apply front brake to stop, you hear a pop, or clunk, that disc has shifted positions, normal.

 

My Fat Bob does it too. I've been told it's normal. Probably twice as loud with dual front brakes.

 

2009 sportster did it, 2010 street bob does it from day one ...

 

Every Harley I've owned (3) has done it. Sounds like a low buzzer going off, and it sounds like it's coming from the reservoir. It is normal, and you will grow to not notice it.

 

My '10 FXDC has done it since day one.

 

Yup, its normal (so Ive been told) and the pitch will change somewhat overtime. You get used to it too.