Fluctuations in the DC frequency range up to 400 kHz are studied in the Elmo Bumpy Torus (EBT-I) plasma. Special attention is paid to the effect of microwave-heated hot-electron rings on the fluctuations, and the fluctuations of the toroidal plasma around the hot-electron rings are found to be reduced to a low level. This reduction is also related to changes in the density gradient, and the predictions of a density-gradient-driven drift wave theory are examined. In the surface plasma surrounding the toroidal plasma, two types of fluctuations are observed: fluctuations with properties similar to those of the density-gradient-driven drift wave and electromagnetic fluctuations localized in the outer plasma along the hot-electorn rings.