avast error or virus?

avast generates an audio signal about the virus, but finds nothing and shows no notification. As if nothing had happened About once every 3 hours.

The first time faced the such, what could it be?

Repair Avast:
Control Panel> Program and Features (Add/remove program)>Select Avast> Select Repair. Reboot when completed
https://www.avast.com/faq.php?article=AVKB204
If Repair doesn’t fix the problem, try the following:
Clean Install of Avast:
https://goo.gl/4Ptzkf

I tried completely uninstall and then download new and install. The result has not changed.

How did you completely uninstall the program ???

start-control panel-uninstall program

That’s not a clean install. Follow the instructions posted.

have you tried making a custom virus check atall? i had a simular issue about a year go, turned out to be somthing hidden in my windows folder but it couldnt remove it without doing a “boot-scan”