In the second last episode Granite State of Breaking Bad, something is very unusual, something which has happened for the first time in the Series.
The intro music is played at the end of the episode.
Why does this signify ?
Just before the episode ends we see Walt drinking in defeat. His life in meaningless with no friends and no family left. He no longer has a purpose in life and he has called the police and is waiting for them to come and arrest him. Then he sees his former Grey Matter partners on TV and they are belittling his past accomplishments. One of Walt's most defining traits is his ego, and that TV interview had just insulted his ego. Now Walt has a purpose in life again. He is, once again, the dreaded evil genius Heisenberg and he is ready to break bad again. Queue the extended version of the intro of the Breaking Bad.