It is dificult to explain why you cannot remember the sound , but here are some parameters that make a tune catchy:
A certain familiarity - similarity to music one already knows - can play a role.
Unfamiliar music doesn't connect well. It's harder to own, especially on first listen. (Picture a teen with an affinity for punk rock listening to his or her grandfather's Tchaikovsky collection -- or vice versa. )
A cultural connection between music and listener can make a tune more memorable. To listeners of a certain generation, for example, the music of the Beach Boys opened up a whole new world of summer and surfing.
Their connection to their audience made the music more appealing.
Repetition also can make a song hard to forget in two ways:
"If you have a hook (a short catchy phrase or passage) in the song, and if that hook is repeated often, that could do it. You might only remember five seconds of the song -- but sometimes that's enough."
Repeated radio play could force a song to become catchy. "You could hear a song 25 times a day. If it has a short refrain that everyone can remember, it will stick, even if it's terrible."
Lastly, a particularly appealing performance of the song may be enough to make it stick in your head.
http://www.physorg.com/news69003006.html