Which 'voice' is the Pasuk referring to?
Rashi: It refers to the sound like thunder that the earth emitted as it swallowed them up. 1
Rashbam: It refers to their screams as they went down. 2
Targum Yonasan: It refers to the cries of those being swallowed up, who proclaimed 'Hashem is right, His judgment is Emes, and the words of His servant Moshe are authentic; whereas we are the wicked ones who rebelled against him!'