That unit is loaded with the noisiest transistors ever (2sc458) In the pre-amp section there are all over TR501-TR511. But these transistors are all past the volume control, and with the noise increasing as you increase volume says that the noise originates before, which is the phono preamp. You can check the connection on the jacks in the back to make sure you don't have a cracked connection or broken ground somewhere by the phono jacks in the back panel, but most probable is that the Phono preamp ic is noisy (TA7122P). While the phono input and outputs go through that function switch, I shouldn't create noise, unless there is a broken connection somewhere, and even that shouldnt create noise. Hum maybe but not noise.
It was a long shot..though.
