Is it normal that turning the volume up/down makes noise (like changing the channel in an old radio) in the E11 ?
1) Unplug the headphone.
2) Turn the E11 on to minimum volume.
3) Turn the volume up to maximum and back to minimum.
4) Repeat step 3 for at least 1 minutes.
5) Listen to E11 and see if the problem goes away.
Absolutely follow clieos good advice to wipe the pot. If still there, try it without an input. If there is no noise without a source, it could be source related as the noise should be there either way if it's the volume control. If in both channels and depending on the circuit, it could be too much DC offset from the source and not an E11 issue.
This can also be caused by a slight amount of DC offset voltage being present as the amp powers up. Usually it will disappear as components stabilize after turning on. Some opamps (in rollable amps) are more prone to this than others, but this is a more or less normal happening.