@leocg ok guys, I found the extension that caused the problem, it was the '' video speed adjuster '' I just had to deactivate it and the background audios didn't happen anymore, nor did strange videos appear in my youtube history, but this is really strange, because I use this extension for a VERY VERY long time and only now it came to cause this malware? anyway, I need to find a replacement for it now.
thanks for your help @leocg