Electrical characterisation is made on low temperature unhydrogenated and hydrogenated in in-situ doped polysilicon thin him transistors (TFTs). The low frequency noise measurements are analysed and related to the static performances of these high mobility TFTs, accounting to the grain boundary potential barrier lowering. The results suggest the existence of two types of excedentary noise sources, probably located respectively, at the SiO2/Si interface and in the grain boundary depleted zone. The hydrogenation, which allows the improvement of electrical static performances, passivates charge traps at the SiO2/Si and grain boundary interfaces and acts in reducing both noise contributions.