What is "Kol ha'Tze'adah"?
Rashi (Shmuel II, 5:24): It is angels walking [on the tree tops. I send them to help you.]
Radak: (Shmuel II, 5:24): I will make a sound to encourage the nation with you. It will sound like walking on the tree tops 1 , as if the angels came out to strike Pelishtim, like it says about Barak "ha'Lo Hashem Yatza Lefanecha" (Shoftim 4:14), and so it says here. Tze'adah is an expression of walking.
Radak (Shmuel II, 5:24, citing Targum Yonasan): It is screaming.
Malbim (Shmuel II, 5:24): The wind will blow, and the tree tops will make a sound, so the Pelishtim will think that there are also [Yisraelim] between the trees.
Radak (citing Shochar Tov 27): Hashem sent them on tops of the bushes, and not in back of them, for Bacha is full of thorns. This shows that when Yisrael are in pain, it is as if there is pain in front of Him ? "Imo Anochi b'Tzarah" (Tehilim 91:15).
