Tinnitus may be like phantom limb: when receiving no input from a group of sensors, the system fills in for the missing information. It's like a microphone with compression: when the speaker stops talking, white noise becomes louder. Your neural system does a lot of filling in for missing sensations, most obviously in tests of what happens when bits of spoken words are removed from a recording: people perceive that the bits were in the recording by triangulating from other information that the bits had been said. Similarly, when hearing loss prevents certain frequencies to be signaled by your sound sensors, the system fills in for the lack of signal in that range. There is still research and some doubt about this theory of what is going on: https://www.nidcd.nih.gov/health/tinnitus