The bike is a 2005 Lemond Croix de Fer.
When I hold the front brake and rock the bike back and forth, there's a low 'clunk' sound that the headset emits. It's not very audible, but I can feel the vibrations in the frame. I've also felt it while riding, when pressing and releasing the front brake.
Is it likely that the headset needs adjustment? Would that be something I could do myself, or does it require special tools?