I had the same problem when I first got my bow. I shot it for a while with the endless loop string that was on the bow when I got it and when I put a new flemish string on it I began to hear a noise like you describe. I finally narrowed it down to a combination of two things, the wax sticking where the string contacted the limbs, and a low brace height causing more of the string to contact the limbs than should have been. I raised the brace height a little and the noise was still there but much less. After about 50 shots the excess wax was gone and no more noise. If you know that your brace height is right, give it a few shots and see if the noise doesn't go away on its own.

Clark