Tawajj us means alert listening or detecting a sound with caution. Surā is travelling by night. Hajs may denote a faint sound or barely perceptible impression, markedly softer than an open shout.
Munaddid emphasizes a voice raised aloud. The antithesis hajs khafiyy ↔ ṣawt munaddid shows the breadth of the camel’s hearing. The verse does not list two different animal calls; it contrasts two intensities of sound.