My HD 7850 fans are clicking? But only at 20% fan speed.

spat55

Distinguished
If I put them up to 40% the clicking noise stops, which has made me think of setting a custom fan speed up at 40% until say 80c. Had the card just under a year now, and it is clocked at 1120mhz core and 5300mhz memory clock. What could this be? Ball bearings maybe? BTW it is a Sapphire standard edition with Dual-X fans.