(Note: I posted this question on AskDifferent (Apple SE) but it's getting no attention so I'm re-posting it here.)
Sometimes when I record myself playing mandolin on my iPhone, using a Rode mic and Rode's app, I get a few seconds of very loud interference. It occurs randomly, perhaps once per hour.
Here is a screen shot of the signal in Logic Pro X:
You can see my mandolin signal behind the noise, those bumps.
What is this? Cell tower interference? How do I avoid it? Airplane mode?
Edit: Here is what it sounds like: