Anyway, I started looking it up and could not find a place where they are said to sing, but only to speak. The exception might be in Rev 5:9 "And they sang a new song, saying, "Worthy are you to take the scroll and to open its seals, for you were slain, and by your blood you ransomed people for God from every tribe and language and people and nation." Since earlier the four creatures seem to be part of the elders (saints) who were worshiping with harps, it would seem fair that they were also singing. It is interesting that the commentators speak of this whole section as men and angels singing songs but singing and song are only used in vs. 9 where later the word changes to that of speaking, not singing. Every time the word for angels is used it specifically says they were speaking.
If there is any reason to think that perhaps none of the angels were singing it might be because of Rev 14:3 and they were singing a new song before the throne and before the four living creatures and before the elders. No one could learn that song except the 144,000 who had been redeemed from the earth. And again in Rev 15:2-3 "And I saw what appeared to be a sea of glass mingled with fire--and also those who had conquered the beast and its image and the number of its name, standing beside the sea of glass with harps of God in their hands. And they sing the song of Moses, the servant of God, and the song of the Lamb, saying, "Great and amazing are your deeds, O Lord God the Almighty! Just and true are your ways, O King of the nations! I don't know how literally to take Rev. 14:3 but it seems to indicate that this new song that is associated with those who have been redeemed can only be sung by those who have experienced redemption.
As I went through the concordance of those who were said to sing or called upon to sing it was pretty much two different groups who were said to sing: the redeemed and creation. Well, Romans 8 says that creation is awaiting final redemption along with the saints. It benefits from the cross as do the elect; the angels have nothing in the cross to sing about. 1 Peter 1:12 says that the angels have a keen interests in the redemption of man. After all, they have been watching all this from the Fall and no doubt find it incredibly interesting. They had been with Jesus since he created them sometime around the creation of all things and have beheld his majesty for thousands of years and in Luke 1 they see him become a babe lying helpless in a stable manger; quite incredible! But they are watching this with no real vested interest. They are not fallen, they do not need a savior, but they will take every opportunity to praise their creator as any worthy creature should.
Now I have nothing against angels singing and they very well might. If they do, it will sound amazing and will only enhance the glories of Heaven. If there is anything my flesh really looks forward to in Glory it is listening to what promises to be the greatest choir ever assembled. It will have perfect pitch and perfect words and best of all it will be sung with perfect enthusiasm. I truly hope that angels will be singing.
But when you see how singing all through the Bible generally is used to praise God for his salvation and that the redeemed are almost entirely the ones called on to sing and then there is Rev. 15:3 that says there is a song that only they can really sing, then we at least have to admit that singing is a gift to man to be used to thank him for the Lamb. I think there are going to be times in which this song of redemption shall be ringing out in Heaven and only from the voices of those who can sing from the heart because they alone have experienced what it is to be pulled from the fire of God's wrath. I wonder if that song will stand out as sweeter than any other singing?
My main point is to the redeemed. Do you appreciate the gift of song and do you take advantage of it when you can? Do you sing loudly at church? Do you sing as though you mean it? Do you ever wonder why false religions have little to no singing and what they have is usually rather morbid chanting. It is because they have nothing to sing about. We do and let us follow David's advice, Psa 98:1 " A Psalm. Oh sing to the LORD a new song, for he has done marvelous things! His right hand and his holy arm have worked salvation for him. Psa 98:4 "Make a joyful noise to the LORD, all the earth; break forth into joyous song and sing praises!"
And perhaps one of the best is Psa 147:1 "Praise the LORD! For it is good to sing praises to our God; for it is pleasant, and a song of praise is fitting." If it is fitting for us to sing praises to the Lord then we need to be a singing people and do it as best we can.