There was an undercurrent to his question that I didn't understand.

他的问题里涌动着我无法理解的暗流。

You don't want to say: Go ... away and break the undercurrent of your voice.

你肯定不想说Go...away，这样会中断你潜在的音流动。

He did not observe her approach, and she stood close to him, and heard his undercurrent of song.

他没有注意到她走过来，她在离他很近的地站住，听到他唱。

Although I really appreciated it, I usually politely declined because there was always an undercurrent of hoping that I might be converted, and I really don't like to disappoint people.

虽然我真的很感激，但我通常会礼貌地拒绝，因为我心里总有一股希望我能转变的暗流，而且我真的不喜欢让别人失望。