Starting a NAS computer server. This is a Synology with 4 HDD hard drives. Fan noise, start disks one by one, then work. UCS Category: CMPTDriv, UIData. Duration: 03:28.
Several beeps of an active sonar. This is a low frequency sonar (long range but low definition). It is a sine wave of 1190 Hz frequency easy to put in loop. In reality, a military submarine usually has passive sonar, more sonar info: en.wikipedia.org/wiki/Sonar. UCS Category: BOATSub. Duration: 00:21.