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I have the following issue with sound on my 2015 Macbook Pro (10.14.6). Every time I plugin my monitor on the Mini-Displayport port (using a MiniDP->HDMI dongle from Club3D), and I plug in my Logitech 2.1 system (old style Z5's) using the headphone jack, the speakers play a constant very high pitched sound. As soon as I unplug the Monitor from the MiniDP port, it goes away. The sound does not change its volume when adjusting volume on the speakers itself.

Any ideas if this issue could be solved within macOS settings?

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  • A common cause for this is electronic interference. What if you plug some headphones into the jack instead of speakers? If you still get the noise, the dongle is likely the cause. Electronic interference issues can't be resolved with software tweaks, you'll need to use a ferrite bead to reduce the effect. en.wikipedia.org/wiki/Ferrite_bead
    – spikey_richie
    Commented Jan 22, 2020 at 14:43
  • @spikey_richie I actually do not. So the issue might be with my Logitech 2.1 system, more specifically the connection cable between the Macbook and the volume adjustment thing from the Logitechs.
    – ffritz
    Commented Jan 22, 2020 at 14:45
  • Yes, or the Logitech device is amplifying the effect of the interference. Does the Logitech 3.5mm jack cable have a thick bump on the lead, as per the link in my first comment?
    – spikey_richie
    Commented Jan 22, 2020 at 14:47
  • @spikey_richie It does not. So you are suggesting getting a 3.5mm cable with a ferrite bead?
    – ffritz
    Commented Jan 22, 2020 at 14:47
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    You could try a snap-on ferrite bead, but it might not help. If your 3.5mm cable can be replaced, you could try one with a ferrite bead present which will reduce and hopefully eliminate the issue. These are inexpensive and might be a simple quick-fix amazon.co.uk/SODIAL-Noise-Suppressor-Ferrite-Filters/dp/…
    – spikey_richie
    Commented Jan 22, 2020 at 14:50

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The most likely cause of this issue is electronic interference caused by your dongle, but audible due to the amplification circuit in your audio device.

The easiest fix is to replace your 3.5mm audio cable to a version with a ferrite bead/choke, or use a clip-on ferrite bead to reduce the effect.

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