Biggest and first thing is to get the brace height correct. Also make sure there is no arrow contact with the riser.After that I like to use leeches (tied in)on the string (experiment with the position, but start with the 1/4 rule). If you want to be more "traditional" use beaver, wool, or muskox. For my recurves, Ieither use bow hushes or felt (or moleskin) or even both (hushes and moleskin) on the back of the limbwherethe string slaps it.

Sometimes if it's still loud you could try a different string material.