I scanned the chapter of The Man Who Mistook His Wife for a Hat which pertains to persistent musical hallucinations. I didn't notice an established term for the condition, whether regarded as hallucinations (in the cases of his patients, which seemed to have been prompted by stroke or other trauma) or as the more ordinary memories, but Dr Sachs does suggest that the conditions are "hypermnesis" or "hypergnosis." Of course, he was more concerned with relating to the underlying pathology than with describing the symptom.