It was the sound of the wings of the living creatures brushing against one another and the sound of the wheels beside them, a great rumbling sound.
KJV
[I heard] also the noise of the wings of the living creatures that touched one another, and the noise of the wheels over against them, and a noise of a great rushing.
ASV
And I heard the noise of the wings of the living creatures as they touched one another, and the noise of the wheels beside them, even the noise of a great rushing.