We study the amplitude modulation of the radial electric field constructed from the  Langmuir probe plasma potential measurements at the edge of MAST. The Empirical Mode Decomposition technique is applied, which allows us to construct fluctuations on temporal scales of plasma turbulence, the Geodesic Acoustic Mode and these associated with the residual poloidal flows. This decomposition preserves nonlinear character of the signal. Hilbert transform is then used to obtain the amplitude modulation envelope of the fluctuating radial electric field on these time scales. We find significant spectral coherence at frequencies between 1 − 5 kHz, in the turbulence and the GAM amplitude modulation envelopes and for the signal representing the low frequency zonalflows. We find evidence of local and nonlocal three wave interactions leading to coupling between  the GAM and the low frequency part of the spectrum.