GRIFFS STI

hi can anyone help with a clunk i have,its from rear and i think is diff related as when i transfer power through switch (adj diff)and run with top light lit it does'nt do it,but when i switch to bottom of light scale every time i ease on'off gas i get i clunck from nsr wheel area,is ther anything serviceable in this area,or has anyone else encountered this,car is a 2000 sti6 type r
cheers
jason