Considerable interests have been focused on the study of turbulent fluctuations in magnetic confinement system, since various theories predict such turbulent fluctuations lead to anomalous transport and energy loss in the transverse direction. Density fluctuations during the formation of the confinement potential with application of electron cyclotron heating (ECH) in GAMMA 10 were studied by using both the multi-channel microwave interferometer and gold neutral beam probe. It is found that low frequency fluctuation, which corresponds to the diamagnetic drift, is suppressed during the formation of confining potential by the application of plug-ECH.