Audio problem: In "Silly Love Songs" during the final song You can hear Blaine singing "I can explain." but in a couple of the shots he is lip-syncing to the "I love you". Next shot is he is back to singing his solo part.
Audio problem: During "Marry You", in the wide shots where Carole is coming down the aisle and the Glee kids are in the background, the lyrics and their mouth movements don't match up.
Audio problem: During the beginning of Rachel's "Baby One More Time" fantasy, the tapping sounds and her pencil's movements don't match up.
Answer: According to IMDb.com, Ian Brennan, one of the "Glee" writers and producers, is listed as the uncredited narrator voice.
Michael Albert