Since GoPro Hero 5, 6, 7, and any newer cameras that are water resistant, they use a special water protection filter for the microphone. When recording, the internal system of the GoPro camera will amplify any recorded audio (even the slightest amount of noise if it's quiet) therefore causing the noise. This issue will occur with any GoPro gimbals in the market.
We recommend to set the audio settings to "Wind only" or related option. To learn more, please visit this page: https://gopro.com/help/articles/Question_Answer/What-is-Wind-Noise-Suppression-How-Does-It-Work