If your front brake arms have some slop from looseness or wear you can isolate their movement by applying the front brake while rocking the bike back and forth. There is usually a little flex in the arms but its easier to see loose fitting parts this way. This can cause some clunking and squealing brakes from the loose brakes vibrating when applied. If the brakes check out OK then it's most likely the headset so you should first check the tightness/preload of the nuts and even though the mechanic used proper press tools for the cups and crown race, if they're just slightly not squared it can cause some clunking that can't be adjusted out.