Hi Vinny,
It may be track bleed, what you're hearing, where a vocal recording may have bled over a little during recording into another track from the phones or similar and deleting the track later you can still hear a little of it because it bled into another track recording. Try soloing your recorded tracks to see if you hear anything like that.
There's no other reason that comes to mind why a track that doesn't exist would still be playing other than it bled into another recorded track, or perhaps if you printed send FX before deleting the track. When you say that you hear it playing "softly", that fits squarely into that scenario.