Windows 10 and 7 has as default an automatic echo cancellation activated. 

This could leads to the problem, that the "other side" can't hear the metronome or other audio signals.

The solution is to deactivate the sound effects or the echo cancellation at least.

1. Right Mouse Click  > Toolbar > Sound Icon 

2. Open Microphone Properties

3. Disable all sound effects or acoustic echo cancellation (at least)