GPU fan clicking when at 100%

hi. i had the fan's speed set to 100% so my card would be as cool as possible. there were no problems for a few weeks and then out of the blue yesterday i started hearing an intermittent clicking sound. it would occur several times per minutes or once an hour. i checked to see if any wires were touching the gpu because, when i turned on the computer for the first time, a wire was touching the cpu fan and creating the same noise.

i lowered the fan to 70% and the noise ceased. anyone know what the problem with the fan is?