In the hot ion mode experiments of the tandem mirror GAMMA 10/PDX plasma, suppression of the flute-like fluctuation, for which the rotation direction is the same as the ion diamagnetic rotation direction, was observed during the axially confined potential formation while electron cyclotron heating (ECH) was applied at the barrier and plug cells for the first time. In the previous experiments, the electron diamagnetic rotation type fluctuations were clearly suppressed with the application of both barrier (B) and plug (P) ECH. We show that the flute-like fluctuation of ion diamagnetic rotation is also suppressed with the application of P/B-ECH.