English-speaking learners often confuse sonar a with sonar como since both translate as 'to sound like' in English. Sonar a generally means 'tener visos o apariencias de algo', in other words it's like 'parecer'. Sonar como, meanwhile, is used to describe the similary between one thing and another. Presence of the indirect object pronoun and absence of a determiner usually mean it takes a. Often 'to sound like' is better translated as 'parecer'.
-(Me) suena a excusa/ amenaza — It's sounds like an excuse (to me) [≈Parece una excusa/amenaza por su apariencia; suele indicar desconfianza]
-¿Qué sonido hace? -Suena como un reloj — What sound does it make? - It sounds like a clock [≈Produce un sonido parecido al de un reloj]
-Tu voz suena como la de mi madre — Your voice sounds like my mum's
-Al aullar, sonó como un lobo feroz [≈Hizo un sonido parecido a un lobo feroz]
→Esa última frase me sonó a lobo feroz [≈Tuvo visos de lobo feroz]
-Parece buena idea/buena persona — It sounds like a good idea / She sounds like a nice person
