Search for "enableUIStaticNoise" in data/config/settings.json and set it to false.
Spoiler
"ui_noise_static":{
"sounds":[
{"file":"sounds/sfx_interface/ui_static01.ogg","pitch":1,"volume":0.5},
{"file":"sounds/sfx_interface/ui_static02.ogg","pitch":1,"volume":0.5},
{"file":"sounds/sfx_interface/ui_static03.ogg","pitch":1,"volume":0.5},
],
},
"ui_noise_static_message":{
"sounds":[
{"file":"sounds/sfx_interface/ui_static01.ogg","pitch":1,"volume":0.7},
{"file":"sounds/sfx_interface/ui_static02.ogg","pitch":1,"volume":0.7},
{"file":"sounds/sfx_interface/ui_static03.ogg","pitch":1,"volume":0.7},
],
},
"ui_noise_static_message_quiet":{
"sounds":[
{"file":"sounds/sfx_interface/ui_static01.ogg","pitch":1,"volume":0.21},
{"file":"sounds/sfx_interface/ui_static02.ogg","pitch":1,"volume":0.21},
{"file":"sounds/sfx_interface/ui_static03.ogg","pitch":1,"volume":0.21},
],
},
Setting the volume to 0 in all those should do it.