I think the first sound effect was accidental, but fortuitous, and after that he planned a little more.
The Hitchcock scene you are thinking of was in his 1929 sound version of "Blackmail". Indeed a very strange and weird scene, but effective.
The murders here reminded me a little of Strangers on a Train (Where a murder takes place at a fairground) and a James Bond flick (I think) where a murder in a sidestreet is masked by a loud carnival along the main street.