I had the same problem with my 150SE/50SE set up. Not so much a problem with noise when the volume control was used but I would hear a loud "pop" from one speaker whenever the mute button was hit or a source change button was used on the preamp.
My problem was resolved by replacing a 6H30 tube in one of the power amps. Now there is no pop or audiblle noise from my system when either the mute or any of the input buttons are engaged.
It looks like you may have tried this already. But if you have any spare 6H30's available, I'd try replacing them in the 75SE and see what happens.
My problem was resolved by replacing a 6H30 tube in one of the power amps. Now there is no pop or audiblle noise from my system when either the mute or any of the input buttons are engaged.
It looks like you may have tried this already. But if you have any spare 6H30's available, I'd try replacing them in the 75SE and see what happens.