Click Settings, find the sound option and click to enter. At this time, you will see an option for screen key sounds below. Just click off the check mark behind it.

Tutorial on how to turn off the dial tone on Huawei Mate9

1. Open "Settings" and click in "All Settings".

2. Click "Call" in "All Settings", and then we can see the option "Dial Key Tone".

3. Click on "Dialing Key Tone", and then click "Silence" to turn off the dialing key tone.