It is shown that in thin-gate partially depleted silicon-on-insulator metal-oxide-semiconductor field-effect transistors (PD SOI MOSFETs) unexpected front-back-gate coupling effects occur when the back gate is operated in accumulation. This is particularly true for front-gate biases (VGF) beyond the threshold for electron valence-band tunneling to occur, inducing the so-called linear kink effect (LKE). As a consequence of this coupling, both the drain current and the drain-current noise spectral density are reduced in the LKE regime. Moreover, for a back-gate bias into stronger accumulation, the LKE regime is shifted to higher VGF in absolute value. Another consequence of the front-back-gate coupling is the appearance of the back-gate-induced (BGI) Lorentzian component in the noise spectra measured for an accumulated back gate in a wide range of VGF. Similar effects have also been detected in thin-gate fully depleted SOI MOSFETs. It is demonstrated that all these front-back coupling effects can be explained by considering the increased body-source leakage currents and, hence, the body-source conductance induced by the accumulation back-gate voltage where the BGI Lorentzian is attributed to the Nyquist noise in the back-gate-induced body-source conductance affected by the capacitive character of the body-source impedance.