Hl2 mystery - Playground memory

I was watching deleted scenes from Training day and as Half-life fan my ear recognized the familiar sound, with help from somebody else i found the last part in Angry kid. Rumors were that the sound used in the game were from attacks on 9/11 this became urban legend over the years. The real source is probably stock sound of playground ambient or its mash up. What do you think? Today () this became my most popular video, in short time catching up to my NAO tribute with over 5000 views . () 420 likes () first 10 000 views. Thank you all.