Ok, so I wasn't able to find chances for it, but it is a random thing that may happen when you're using the Pokeradar and you end a battle with a Pokemon. While not proven to increase shiny chances, it appears people have had better luck with getting shinies while the faster music plays.
Another new change is that, after battle, there is a slim chance that the music will change to a more up-beat music. When this occurs, there is a higher chance of encountering a Shiny Pokémon.
As for resetting your Pokeradar for it, as I said, after a battle it will activate, so I don't think that resetting it affects the process, I believe it just happens right when you end a battle with a Pokemon.
Hope this helps! :)