Had this on 3 puntos, all three times, same problem.
It was the handbrake cable squeeking in its rubber grommet. If you look just in front of the rear wheel, you'll see where the handbrake cable clips in to a metal clip and protected by a rubber sleeve. Unclip it, slide the sleeve down, grease the outside of the cable and slide the sleeve back in to position. Prise the clip open so its a very loose fit around the cable and just use a loose cable tie to hold it to the clip. problem will be solved for years.