A group of experts devised a technique dubbed DiskFiltration to exfiltrate data from air-gapped networks relying on acoustic signals emitted from HDDs. The technique was devised by Mordechai Guri, Yosef Solewicz, Andrey Daidakulov, and Yuval Elovici from the Ben-Gurion University. The attack method is effective in a range of six feet, it could be used to transfer 180 bits per minute, a speed that could allow ex-filtrating a 4096-bit key in about 25 minutes.”]
Source: https://securityaffairs.co/wordpress/50245/hacking/diskfiltration-air-gapped-networks.html