Sound marks that are unlikely to be accepted without evidence of factual distinctiveness (secondary meaning) include:
Very simple pieces of music, such as those consisting of only one or two notes (e.g., the ‘ding-dong’ of a doorbell).
Sounds that are part of the common domain (e.g., "La Marseillaise" or "Für Elise").
Sounds that are too long to be considered as an indication of origin, such as an entire song.
Sounds typically associated with specific goods or services, like the sound of an engine for vehicles in class 12.