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I bought a pair of Brainwavz M1 headphones today and when using them with my Macbook air there is an intermittent buzz regardless of whether or not there's sound playing and irrespective of the volume of the air.

I'm fairly sure that it's 50 Hz noise from the power but curiously when I unplug the charging cable the noise is still there but not quite as loud.

If I touch the body of the laptop the humming stops whether plugged into power or not.

The headphones have a rated impedance of 32 ohms.

Is there anything I can do to stop it?

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Most of the Macintoshes I've had over the years have had a buzz in the headphone port. It is especially noticeable with low impedance headphones. Some have even had a click when the sound is turned on (i.e. when an alert sound plays, or a song is started in iTunes).

You could try taking it to the Genius bar, they might replace it if it is still under warranty. There could be a short somewhere, or it could just be considered "normal" which is why audiophiles use digital output.

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  • Not what I wanted to hear but thanks for the reply. What do you mean by digital output though? Like a USB DAC?
    – JimR
    Commented Oct 18, 2013 at 5:51
  • Exactly. The headphone jack of recent MacBooks has an optical digital output so you could send the audio data to an external DAC either via USB, which are in short supply, or the headphone jack via optical SPDIF.
    – Ɱark Ƭ
    Commented Oct 18, 2013 at 12:43
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You said the humming stops when you touch the machine, which reminded me of another issue: in some situations, some people can feel a "tingling" sensation when they touch the casing of a portable Mac which is connected to an ungrounded power supply.

So, an idea here: plug the power supply in, but make sure you are using a grounded plug on the power supply. There are some more details in the answers to this question.

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  • I'm not feeling a tingling sensation and unfortunately I'm in Europe, I don't think it's possible to have a ground connector on the two prong plugs here?
    – JimR
    Commented Oct 18, 2013 at 5:51
  • Some people can't feel the tingling sensation. What country are you in? I don't know much about European plugs (I'm in the UK) but I can see at en.wikipedia.org/wiki/AC_power_plugs_and_sockets that certain European connectors have earth pins on the side of the round plug (see eg en.wikipedia.org/wiki/File:Schuko_plug_and_socket.png). Of course this is just an idea of mine: I might be incorrect, but I'm thinking that grounding your Mac would reduce the hum.
    – Ashley
    Commented Oct 21, 2013 at 11:02
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I had this exact problem. It's a grounding issue. I'm guessing you're plugged in using the 2-prong plug? Use the 3-prong plug and you'll be golden.

It's a subtle issue, but what's happening is that you created a ground loop by not using the ground prong on your charger. Your USB-C cable is acting like an antennae, and it's leaking RF noise into the air, creating what Shure calls a "hum field", or an inductive loop, which the microphone is picking up.

I was never able to figure out why the noise would disappear when I touched the body of the laptop though. Maybe the body is acting as a ground and absorbing the EMI?

A little trick is that you'll notice that the amount of noise will increase and be very stable when you touch the metal shield of the USB-C connector.

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