clicking and or ticking noise when i brake?

clicking and or ticking noise when i brake, what would cause this any one have any ideas?
it's just when i brake, its a 91 xj 2wd.
thanks for any unput.
Legacy.

Is the noise coming from the front or rear? Also,with what amount of foot pressure does it make it? Is it a constant click or does it just click once when you press the pedal? First thought, possible master cylinder. I really need to read the dates on these posts .......