Brakes squeak

[WillUK]

Hi there. Fitted genuine front discs and pads 2000 miles ago, and all of a sudden squeaking under light braking only. no squeaking under heavy braking. Ate plastilube has been used to the back of the pads but it didnt help. it was no squeaking till last week and like i said 2000miles on them already. Where should I start my investigation?

its touran 05 plate

many thanks