Few days back I heard an audio playback “Congratulations you have won” on my laptop and since then it just persisted. Normally it used to happen when I am surfing web, suddenly a loud audio will play in background saying “Congratulations you have won”. After a day or two I noticed that my youtube page was not being displayed properly, i.e. I noticed some extra bits in the page that should not be there or they did not fit in with the rest of the page design.
This got me convinced that I have some malware or virus on my computer and I checked my computer for malware and viruses but could not find anything, over the time the playback audio just became more and more frequent like once every 5 minutes.
Eventually I found that this is because of one of the extensions that are installed with chrome, and I disabled that extension as below :
And my computer and youtube were restored in correct state, no more annoying audio!