Fan only works when at 80%

[Rocwen Colondo]

Hey guys,
I have radeon hd 7870 xt sapphire with two fans , the other fan doesnt work totally , even at stress test or when using intensive softwares or gaming .. but i noticed when i manually set the fan speed to 80% using speedfan software the other fan works .. but only then .. it doesnt work automatically at load doesnt work at lower than 80% and doesnt work when i put it at 80% through bios .. so any suggestion to how im going to fix that ?

 

[Rocwen Colondo]

Keeping fan speed at 80% seems too noisy so anyway i can make it work at lower speeds?