Getting a choppy helicopter sound in the back ground of video recording that I make on my iPad Air 2. Any idea what could be causing this?

Every time I make a video recording on my iPad Air 2, I hear this strange sound like helicopter blades.Att first I thought it was coming from the building that I was in, but I can hear it in other recordings where the ambient sound is low. I know now that this sound has been there since I bought my iPad Air 2 in Febuary. Any ideas on what it is, and how I can Make it go away? My iPad seems to work just fine otherwise, I only have this problem from audio playback that has been recorded using the built in microphone. Thanks.