Noise of a-Si:H p-i-n diodes (5 approximately 50 mum thick) under reverse bias was investigated. The current dependent 1/f type noise was found to be the main noise component at high bias. At low bias the thermal noise from a series resistance of the p-layer and of the metallic contacts is the dominant noise source which is unrelated to the reverse current through the diode. The noise associated with the p-layer resistance decreased significantly on annealing under reverse bias, reducing the total zero bias noise by a factor of 2 approximately. The noise recovered to the original value on subsequent annealing without bias. In addition to the resistive noise these seems to be a shaping time independent noise component at zero biased diodes.