Are you shooting with a glove or tab? Try a tab.

Do you have the string silencers positioned in the right place? Some work better than others but basically they are all about the same.

As already said brace height could be causing some of it.

Do you have a little "Mole skin" under the string groves ?

After all this, if you are still getting the "Twangs", sorry but you are plucking the string.

Concentrate on the release, make it relaxed and smooooth.

Changeling