2006 Dodge Caravan SXT, 3.3L V6 engine, 24000 miles

Weve recently had the front disk brakes serviced after less than a year of ownership. Weve been told by a friend to have the dealer check the master cylinder as there might be an uneven distribution to the front discs. The dealer tells us that this is a maintenance item. Just recently were hearing a single sharp knocking metallic sound when we sharply apply the brakes even at low speed. We also have a similar single knocking metallic sound when we shift in to reverse while parked.

Do you recongnize a chronic problem? Also, have these cars had a cronic problem with the master cylinder? Any help with our problem?