Rashi: I heard that the angel called the Ofan 'Galgal'.

Radak: It does not teach that Ofanim are called Galgalim. Anyone who knows language knows this, just like Beged and Simlah are the same! It says "v'Ofan Agalah" and "v'Hamam Galgal Eglaso" (Yeshayah 28:27-28)! Rather, it teaches that the Navi heard a voice call to them. Also "ha'Dor Atem Re'u Davar Hashem" (Yirmeyah 2:31) is calling. All actions mentioned of the Ofanim are based on the commander's command and desire; it is as if he calls to them 'do such and such.' The Keruv commands the Ofan, but not via a voice or organs of speech. Hashem made the Navi hear a voice to understand [that there is a command]. The same applies to "v'Kara Zeh El Zeh v'Amar" (Yeshayah 6:3).

Malbim: The Galgal is the feet of the Chayos, which roll the Ofanim. Do not say that they roll them via physical contact, for there is no body. Rather, it is via voice and command; they move them intellectually.