All perfect praise be to Allaah, the Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His Slave and Messenger.
Abu Moosa Al-Ash'ari said: “We were with the Prophet and when we approached a valley, we used to raise our voice saying 'La illaaha illa Allaah', and 'Allaahu Akbar', so the Prophet told us: "O people, take it easy (i.e. lower your voices), indeed you are not calling upon a deaf or a distant one. but One Who is with you, He is All-Hearer and, Ever Near (to all things), Blessed be His Name and exalted be His Majesty." [Al-Bukhari and Muslim]
Accordingly, Imaam Muslim entitled a chapter in his Saheeh: "The chapter of desirability of lowering one’s voice when mentioning Allaah except in cases where there is Sharee’ah-based evidence to raise one's voice, like when saying the Talbiyah.”
For more benefit, please refer to Fatwa 90031.
This Hadeeth by Abu Moosa Al-Ash’ari is evidence that one should not raise his voice when mentioning Allaah. What is meant here is to exaggerate in raising the voice like in the case of Athaan or Talbiyah. Al-Haafith Ibn Rajab in his explanation of Saheeh Al-Bukhari said: “What is meant by the prohibition of raising one's voice when mentioning Allaah is exaggerating in raising the voice; as the one of them was shouting 'La ilaaha illa Allaah' and 'Allaahu Akbar' very loudly; so the Prophet told them: ''O people, take it easy (i.e. lower your voices), indeed you are not calling upon a deaf or a distant one." and he made a gesture with his hand that they should be calm and lower their voice.”
Also, Ibn Rajab mentioned a narration by Ibn Seereen that he disliked raising the voice except in two cases: the Athaan and Talbiyah, and he said commenting on this narration: “It means – and Allaah Knows best – exaggerating in raising the voice, like when the Mu'aththin raises his voice (when calling the Athaan) and the one who raises his voice when repeating the Talbiyah.”
Based on the above, one should not raise his voice in such protests and meetings.
To know the ruling on demonstrations in general, please refer to Fataawa 143795 and 97197.
Allaah Knows best.