Here is Paul Whiteman and his band playing Shakin' the blues away - recorded I belive in 1927. Interestingly at the very start of the disk you can hear two distinct buzzes just before the music starts - I left these in - I assume that they were a signal that the recording aparatus had been started?
Ive never heard these sounds on other disks either. I agree they are faint and when acoustically playing the disk they cant be heard. I have done an extract of that part of the disk and increased the volume