Is it pronounced while climbing? I had this problem with my 98 Nishiki road bike, the bottom bracket was out of adjustment (cup and cone type). You will probably need a cup wrench to and maybe a lockring tool, I was able to do mine without the lockring tool. It is not a hard job but requires some patience when adjusting the cup.

http://www.parktool.com/blog/repair-...racket-service