There's a lot of things you can do to get a bow quiet, or at least quieter. Cat whiskers are my favorite silencer--I tie mine on around the string with serving material or you can also use dental floss or some other strong thread. This keeps them in place when you unstring the bow, and you can move them up or down the string to tune them. Moving the silencers up or down the string even an inch can make a big difference on some bows.

As was already noted, the first step is tuning the brace height. Find the quiet spot with no silencers attached. Add silencers at the 1/3 or 1/4 points on the string (or a small set on both, if it has a lot of vibration). Keep them fairly small--big silencers can make their own noise and slow down your bow.

Other things that can affect bow noise: along with string slap, a nock that fits too tight, arrows that aren't the proper spine (can slap the riser as they pass), a poor release, and some tabs make a slapping noise.

Chad