We have a 2005 Mazda 6 Sportwagon, that is a nice car just love it. My wife drives it we've owned it for a year. This weekend I have been driving it and have noticed this metal on metal sound(tap or clunk)when the brakes are applied ONLY the first applying of brakes. The two times I have heard it are as follows if this helps:
1. Pulling out of the driveway and stopping at end of driveway and BOOM metal on metal sound(tap or clunk) ONLY once. Didn't hear it after that at all, drove to Hospital to have our newbaby delivered, parked in parking ramp. Stayed for 3 days, let it sit.

2. Pulled out of parking ramp spot driving toward exit and used the brakes to slow down andBOOM metal on metal sound(tap or clunk) ONLY once and not again(10 mile drive home).

3. Got home from hospital, had wagon parked for quite a few hours and pulled out of the driveway and used brake to slow down at corner to turn andBOOM metal on metal sound(tap or clunk) ONLY once and not again. I drove around the block and now have it parked in garage.

Tomorrow have to go grocery shopping, see what it does then.

It is one quick metal on metal hitting sound(tap or clunk) when brakes areFIRST applied, after the wagon has been sitting for a while.It is not a squeaking or squealing noise.

KB