Why does it say "Lefanav Ragzah ha'Aretz"?
Radak: When they came, the land was agitated in front of them. This is a Mashal for the great affliction, and also "Ra'ashu Shamayim" and "Asfu Nagham." Verses speak like this - "Chashach ha'Shemesh b'Tzeiso" (Yeshayah 13:10).
Malbim: Hashem will do this Himself, without the Ma'arachah, therefore the land will be agitated.
Why was Shamayim noisy?
Rashi: Due to the punishment that will come on Yisrael, they are angry and make noise.
Malbim: The order of the Ma'arachah will cease, for it will be Hashgachah from Hashem. In Yeshayah (13:13), it says "Al Ken Shamayim Argiz v'Sir'ash ha'Aretz mi'Mekomah" - Hashem will order the Ma'arachah and change it so that it will destroy Bavel. Here, Hashem will do it without the Ma'arachah.
Why will the sun and moon darken?
Malbim: They will cease to conduct the world.
What is the meaning of "Asfu Nagham"?
Rashi: They gathered their light [Radak - to themselves, so it was not seen. The same applies to "Esof Yadecha" (Shmuel I, 14:19) and "va'Ye'esof Raglav" (Bereishis 49:33).]
Malbim: They will not have any influence [on the world] at all.