Clean up audio: Interviews inside plane; loud engine noise

I have about 60 seconds total of audio... interviews conducted inside a small airplane. It was through a noise-canceling headset, but the background noise of the airplane still tends to drown out the voices. I am looking for someone to reduce the engine noise and amp up the sound of the interviewee. The engine noise is a static, low frequency hum. I've tried noise reduction on Audacity and Avid but the voice sounds robotic. I need to maintain voice integrity while bringing down the engine noise.