Maybe he had tinnitus (interesting reading):
https://steemit.com/health/@mindover/what-the-hell-is-that-ringing-noise-the-torture-of-tinnitus

Wiki says:

Tinnitus is the hearing of sound when no external sound is present.[1] While often described as a ringing, it may also sound like a clicking, hiss or roaring.[2] Rarely, unclear voices or music are heard.[3] The sound may be soft or loud, low pitched or high pitched and appear to be coming from one ear or both.[2] Most of the time, it comes on gradually.[3] In some people, the sound causes depression, anxiety or interferes with concentration.