If you hear a hum or buzz coming from the loudspeakers when connected with the WiiM Mini's analog Aux-out port, there are two possible causes depending on what type of hum you are having. 

Type 1: 120Hz hum/buzz 

It's typically caused by the ground loop problems. Please use the separate power adapter for WiiM Mini instead of directly plugging your USB-C cable into the USB port of your DAC/amplifier/speaker. If it still exists, please find a separate power bank to see if this issue is gone. If it's, it's actually caused by the ground loop problem.  

Type 2: 60Hz hum/buzz 

Poor shielding, cable problems, or close proximity to strong magnetic fields typically cause it. 

You can also try using the digital optical port to see if the noise is gone. 

If nothing above works for you, please send us feedback via WiiM Home App so we can take a look at your issue further. The steps are selecting the Settings tab > Feedback

For more information about hum/buzz noise, there's an excellent tutorial from PSAudio.