Low frequency noise, LFN, was studied in three sets of n-MOSFETs, with silicon nano-crystals, Si-nc's, imbedded in the gate oxide, in planar layers placed at distances tnc=1.2, 1.5, and 2nm from the Si/SiO2 interface. The power spectral density of the drain current, Id, fluctuations, SId(f), was measured on the devices with the Si-nc's and without (reference samples). SId(f) measured on devices without Si-nc, was of 1/f type. The spectra in the devices with the Si-nc's, were accounted for by a superposition of a 1/f noise and a packet of Lorenzian lines, peaking at some mean frequency, fnc, found to depend exponentially on tnc. Such a dependence implied that the charge capture and release on the Si-nc's is governed by a direct tunnelling, with a characteristic tunnelling length, λ. From the data obtained on devices with three different positions of the Si-nc layers we could extract the value of λ, found to be equal to about 0.1nm, with a slight dependence on the applied gate voltage. The same constant is also involved in the 1/f component of LFN which is interpreted in terms of a carrier number fluctuation (McWhorter) model, where surface potential fluctuations result from the charge capture/release on traps distributed in the gate oxide. Finally, the frequency dependence of SId on tnc is explained using the standard model of carrier number fluctuations, generated by trapping/release on oxide interface traps and Si-nc's.