Everytime I brake from a fast speed like say 40 kmh it makes this very faint squeaking sound, any suggestions what it may be?

 

It could be any number of things, including pad composition, excessive pad vibration, low pad lining, dust shield contact, etc.

The best thing you can do is to pull the wheels off and visually inspect the brakes yourself. Make sure you have enough lining (3/32" or more on all pads) and that nothing is rubbing.