This sound generally indicates loose front suspension components.
You may be wondering what the correlation between braking and a vehicle's suspension is. Well, imagine you're driving and then you step on the brakes. Immediately, the vehicle's weight is "thrown" forward, sort of "onto" its front suspension.
So, any loose front suspension components will really "make themselves be heard" (i.e. clunk) when all that weight is thrown onto them.
What to do?
Take this vehicle to an AAA approved shop (preferably) and ask the mechanic to inspect the front suspension. Explain the logic that we explained to you. Since the car has less than 50,000 miles on it, the suspension components are probably just loose and not worn.
