Retumbando comes from the verb retumbar, meaning to reverberate, echo, or boom. It's a vivid and onomatopoeic word that describes a deep, resonant sound.
In the song, the artist sings, "Tus gemidos en mi mente siguen retumbando" (Your moans keep echoing in my mind). This word powerfully conveys how the memory of a sound lingers intensely, almost physically, in his thoughts, making it a memorable and evocative choice.
Lenny Tavárez's "A 100" is all about a guy who just can't get over his ex, even though he's trying everything to move on! He's constantly hearing her moans in his head, saying, "Tus gemidos en mi mente siguen retumbando" [Your moans keep echoing in my mind]. He's out trying to distract himself, going "a cien con una loca que lo está enrolando" [a hundred with a crazy girl who's rolling it up], but deep down, he admits, "Por mi mai que todavía yo te sigo amando" [I swear to my mom that I still love you].
He's smoking to stop thinking about her, and even though he's got "una zeta y dos babies" [a Z and two babies] every week, he still thinks about her constantly. He's begging for another chance, asking, "Baby, dame otra oportunidad" [Baby, give me another chance], and wondering how to forget all their intimate moments. He tells her, "Tú eres mejor nota que el nota" [You're a better high than the high], and that she's his ultimate fantasy, making him feel like he's in ecstasy. He really wants her back, saying, "Ma, tú me tienes pa ti, por favor no me hagas rogar, que te quiero pa mí" [Ma, you have me for you, please don't make me beg, I want you for me].