Halo 3 Controls say Vibration - Disabled in the Menus, but Controller vibrates on every trigger pull. I’m not sure how many people enjoy playing with vibration on, but I don’t because it is highly distracting and a huge battery killer.
if you go down a little bit further you will see an option called ‘Impulse triggers’
Disable this and it will solve your problem 
Thanks. Not sure why I didn’t think to scroll down