How long have you been playing? I ask this because I think it comes more as a natural thing in the end than a particular technique. It is pretty unconscious in the end, but I htink it involves using both the right hand and left hand to dampen the string that you are about to let go of... I remember when I started playing blues bends and stuff really hating that I would always make noise when I let go and went on to something else, but in the end I think it just goes away. If anyone can come up with something better than this feel free to add, but I have a feeling it just is something you end up doing by yourself. I also think it has to do with finger dexterity that you gain the ability not to hit other strings etc. Myabe if you don't let go of the string completely when you release a bend, but mute it with your finger before letting it go. Hope this helps in some way.