The noise that the snake repellers make has 2 purposes.
1. It is the noise that actually produces the vibration down at the tip of the snake repeller.
2. The noise lets you know that thesnake repeller is working.
The noise comes up the stake unit and out into the atmosphere, you can put a piece of rag or similar down the tube and this will quieten the noise level. It has no bearing on the operation of the Snake Repeller.
Try this and see how you go.