I have an Arduino Nano connected via USB to a Mac Mini. When the LEDs come on, an external speaker connected to the Mini starts to hum/buzz quite loudly. If the LEDs are turned off, the buzz stops.
The speaker and the Mac mini are both powered independently, and are plugged into one wall socket, while the 5V power supply to the LEDs and the Nano is plugged into a different socket (of the same outlet).
What could be causing the buzz and what are the possible remedies?