I'm starting a podcast that involves a lot of over-the-phone interviews. I've been using a Blue Nessie USB microphone to record both my voice and my iPhone 6s speakerphone simultaneously. The problem is, whenever I start a call, the microphone records a steady, quiet crackling sound. When I hang up, the crackling stops. Does anyone have any idea what might be causing this or how I can make it go away? Thanks a trillion.