Correct.

"And I saw another strong angel coming down out of heaven, clothed with a cloud; and the rainbow was upon his head, and his face was like the sun, and his feet like pillars of fire; ²and he had in his hand a little book which was open. And he placed his right foot on the sea and his left on the land; ³and he cried out with a loud voice, as when a lion roars; and when he had cried out, the seven peals of thunder uttered their voices. ⁴And when the seven peals of thunder had spoken, I was about to write; and I heard a voice from heaven saying, "Seal up the things which the seven peals of thunder have spoken, and do not write them." Revelation 10:1-4 (NAS)

John was told by a voice from heaven to seal up what the thunders spoke...and not to write them down.  It is unknown to us (as readers of the Revelation) what they said.

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