To turn off Growl Notifications altogether, navigate to Account Settings under your profile icon in the bottom left corner. Disabling Growls will turn off the sounds that go with it.

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As an additional workaround that does not require disabling any settings, you can use the Chrome browser, right-click on any open Helpshift tabs, and select ‘Mute tab.’

To learn more about Growl Notifications, see What Are Growl Notifications, And When Do They Appear?