1)
Why are the mountains making noise?
1.
Malbim: It is as if the water returns to cover the land; it will be a plain and valley, like initially.
2)
What is the meaning of "Hiskalkelu"?
1.
Rashi: They were uprooted and cast from their place. This is like "Kilkal ba'Chitzim" (Yechezkel 21:26).
2.
Radak: It is known how Chazal explained this 1 .
3.
Radak citing his father: They were light, therefore they made noise. Their weight stands them [in place; when they are heavy, they are quiet.]
1
Eichah Rabah 1: The mountains and hills cried.
