In order to record system sound Movavi Screen recording products use a special virtual device that mirrors the system sound to speakers and, thus, the sound is possible to hear on a record. 

The virtual device installed along with the Movavi application and is currently invisible at your system sound settings.

In all the Screen Recorder versions earlier than 5.4 the speakers icon on the task bar used to turn gray because Movavi Sound Grabber visibly took control over your sound device. 

There are certain cases when the sound might be lost:

1) The installation error might have occured.

Please try re-installing the Sound Grabber application. 

Please close your copy of Movavi screen recording application prior to reinstalling the sound grabber.

How to remove the Sound Grabber utility

After that, please install it once again using this instruction

2) Some applications take control over the sound as well. 

If you use any third-party audio applications such as Sound Flower or similar, a conflict might occur.