There could be one of two things or both, If you have aftermarket pads, which at that year car I would think so, there is a slight free play where the pads stay held buy the caliper. When the brake is applied the little free play it has is taken up this is the click sound when it moves up under pressure. Also what I find is where the pad rides on the caliper it sometimes groves it a little on the older cars and will make a slight click noise. This one is more rare but I have seen it happen, None of this is effected for your bake performance but can be fixed if it bugs you.