I guys i think i found out on to turn the dont sink off. The sound that we hear is from default sound of FSX the wavw file is "GPWS dont sink"  by moving the file elsewhere the sound id not there anymore . I guess FSX  see the sink rate of capt sim a/c differently , anyway i can live with others  default a/c of FSX not having the sound , and flying the 757 without that sound on final.
Hope it works for you .

Jean
Air traffic controler ,and pilot   :D