Source: The Great Interpretation of Dreams (Ibn Sirin)
Singing with an ugly voice in a dream indicates a losing trade or false speech that is not heard.
Source: Perfuming Humanity in the Expression of Dreams (Al-Nabulsi)
Singing with an ugly voice indicates worry, grief, and scandal.
Source: Signs in the Science of Expressions (Ibn Shaheen)
Singing with an ugly voice is interpreted as worry. Whoever sees himself singing with it will be afflicted with worry.