If the AMP1 is connected to the mains via the power cable, you can hear a quiet, high-frequency ticking directly in the device, even if the AMP1 is switched off. This noise comes from the switching power supply and is completely normal.
The mains switch of the AMP1 is located in the secondary circuit. As a result, when the amp is switched off - as with many modern devices - there is no proper disconnection from the mains. Strictly speaking, the AMP1 is then on standby. Therefore you can hear the ticking of the switching power supply, even if the AMP1 is not switched on.
Note: This noise can still be heard for a while after the AMP1 has been disconnected from the mains.
If that bothers you, you should use a switchable power strip with which you can completely disconnect the device from the mains by switching it off.