(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:

audio interference

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:

  • It's probably the phone checking in with base stations from time to time. Airplane mode and switching off all communications like wifi, bluetooth, nfc... would be the first thing to try. Jul 16 '19 at 21:25
  • Can't tell just by looking at it. Post it to Soundcloud. Phone "hunting" [when it's checking for nearby towers] used to be a big thing in the 90s -most studios had a strict 'phones off' policy - but they seem to be better these days. I can only describe it as a "bipeddy-bip dah-di-dah" noise, similar to, but not the same as a modem handshake.
    – Tetsujin
    Jul 17 '19 at 7:31
  • @Tetsujin Soundcloud clip added
    – Eric O
    Jul 17 '19 at 20:53
  • Yup, that's definitely the phone 'hunting'. Alphonso has already dropped it into an answer, with the 'fix'.
    – Tetsujin
    Jul 18 '19 at 6:39
  • While not definitive, I recorded for two hours in Airplane Mode with no interference.
    – Eric O
    Jul 27 '19 at 2:28

Yes, that is your phone broadcasting. That sound is sometimes produced when a phone is sitting near or on an amp or powered speaker. As Your Uncle Bob says in the comments, switching to Airplane mode should should stop the broadcast.

  • I believe this is correct. I have been experimenting with turning on Airplane Mode, and the problem does not occur. While not definitive, at least anecdotally this seems to confirm the suggestion that it is the phone broadcasting "I'm here!" Thanks
    – Eric O
    Nov 26 '19 at 18:11

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