This is a link to youtube where the producer of Jason Upton's (a christian artist) album explains that as they are recording the song FLY for his album that Jason is on stage alone singing with his piano when you hear three part harmony and the other voices on the track is an actual angel singing with him and it was recorded on audio! They say angels don't sound human in their speech and this voice doesn't sound human but is very audible. During the taping a little boy says to the producer there is a 12ft angel standing behind Jason on stage but no one believed the boy because they couldn't see the angel until they heard the recording later and the additional male sounding voice.
The second link is the actual song and you will hear the angel voice come in the background about 5:12 into the song. You can't mistake it! Totally amazing!!
It sounds like a male voice.
He comes in louder at 5:20-5:24
Again @ 5:30-5:33
Again @ 5:38-5:44