@onder
If you plug your Roku Streaming Stick into wall power (using a 5volt 1amp charging adapter) instead of your TV's USB port, the Streaming Stick will no longer keep turning on/off when your TV turns on/off. This will stop the sounds you are hearing.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102