What he meant was the sound you get when there's a response for USSD code that you run.
For example, when you check balance / account status using eg. *126#, there will be a notification sound played (in my case, the default sound, Life is Good) when you receive the response from the carrier company.
I read somewhere, that it affects only D802 with HK rom. Can anyone else confirm?
Sent from my LG-D802