The front disc on my motorcycle emits a low pitch squeaking noise when I'm pulling up to a complete stop (almost like the sound train brakes make when pulling up to a station). This only happens when I am going rather slow - if I use the brake at high speed it's fine.
Brake itself feels fine, responsive and smooth and I've felt the rotor for wear and it feels fine.
Should I be concerned about this at all?
Most brake pads use some sort of shim or spring to stop the pad from oscillating,aka making noise. What generally causes the noise is a small amount of movement by the pad at a very high frequency. Manufacturers eliminate this with shims,springs or a soft material that acts as a dampener. It is possible that one of these has failed from time,use or enviromental exposure. Another possibility is the pads are contaminated with oil splashed up from the road.The pad material is a blend or compounds that offer different traits in terms of wear,stopping power,noise etc. You may have a pad in which the material was not blended evenly and you are encountering hard spots that is causing the squeal. Another possibility is that the pads are equipped with a wear sensor. This is a small metal tab attached to the pad that rubs on the rotor when the pad is worn to the minimum usable thickness. The tab will rub at all speeds but may be audible only at slower speeds.
How long have the pads been on the bike?
Check for Glazing, wear and dust build up. You could also have a small stone lodged next to the pad in the caliper.
Are the brake discs scored? Excessive scoring can cause this noise too.
When dealing with issues with brakes - never leave them alone. Always check them out, if it turns out to be nothing then you've lost a few minutes of your life, if it turns out to be something big you may have saved your life.
Had the same problem with my bike took it to the local mechanic Turns out the break pads had worn out a lot and needed replacement and the brake piston seal had been overextended so the seal was damaged too
I had the same symptoms. I fixed it by rotating the front wheel freely by hand and cleaning the brake pads with a jet of water.
If you brake is new. It’s only cause the piston are dirty. It’s happen to me. In my case it’s was dirty. I took some brakes cleaner. And clean my brakes and the pistons with the calliper with a soft brush. And then no more sounds. Check the pics. Thanks 
