I'm asking on behalf of my partner although I have a Mac as well. Partner has a Mac Mini running OSX El Capitan version 10.11.1. A few weeks ago my partner began hearing a strange laughing baby sound. It would come on at random intervals without him doing anything. We went to Accessibility to make sure Voice Over was off, which was suggested by someone else on a different forum. This didn't change anything. The sound, which was a sort of "hehe", would come on unprompted regardless of what programs were open or if the computer was touched at all. He even called Apple Care and they couldn't figure out what was wrong. He ended up uninstalling the operating system and reinstalling it, but managed to save his files on an external drive. But that sound came back. Luckily, it's only the sound that he's been dealing with. His files seem fine, nothing else is happening, etc. I ran Malware Bytes and Avast, did full system scans. But neither program turned up anything. I still think it's a virus though but I'm trying to figure out what else we can try. Anyone else had a similar problem? What might be the fix? He's thinking of taking his Mac Mini into the Apple Store for them to do a scan but I'd like some perspective before he tries that. Thanks.