No, you weren’t hearing things: Those were the voices of Ewan MacGregor, Frank Oz and Alec Guinness that we heard during Rey’s vision in The Force Awakens, J.J. Abrams confirmed to Entertainment Weekly.
Ewan McGregor came in to record his part (after cartoon counterpart James Arnold Taylor took a shot at it,) as did Frank Oz. Guinness’ “Rey” was isolated from existing audio:
As they worked on editing the dream sequence, Bryan Burk, a longtime Bad Robot collaborator and one of the producers of the film, surprised Abrams one day with the gift of a single word: Obi-Wan Kenobi’s voice saying the name “Rey …”
“I said, ‘That’s cool, is that the thing from Ewan McGregor?’” Abrams recalled. “He said ‘No, we took a line from Alec Guinness saying ‘Afraid.’”
Not only that, but the lilt in his voice from that truncated word happened to fit exactly what Abrams had in mind. “They cut it, and you hear the performance – he’s saying it the way I would have begged Alec Guinness to have said it. It is so crazy perfect,” Abrams says. “So when you hear Obi-Wan talk to Rey it is both Alec Guinness and Ewan McGregor doing the voice.”
Taylor and several other familiar voices can still be heard in various parts around the film – but I’ll leave the specific IDing to those more well-versed in the cartoons than I.