Is the "clunk" on the outside or inside your hip? I have the same thing on the "outside" off and on, but think mine is from the iliotibial band. If i am not careful, i get pain on the outside of my hip and into my knee. Some things i do that seem to help:
the stretch in
this article, but i've always done it with the arm of the side i want to stretch raised over my head (zach's stretch is good too!)
very light dynamic warm-ups before practice raising the leg with the knee bent first--straight leg dynamic raises made me almost unable to walk for about a week
watching leg position when coming DOWN from a kick--also i found that making sure the quads and abs are engaged is helpful, instead of just swinging your leg down without thinking
massaging the itb with the heel of my hand from the hip to the knee--this works like magic
of course, this may not be your problem, so you should find someone who can identify what is going on