There used to be something called print-through on tapes. When tapes were kept unused for too long, the magnetic signal from the second layer of the winding would slightly magnetize the top layer tape. If the top layer was blank, as at the beginning of a song, you could hear the first bars of the song as a faint print-through signal on the blank lead-in before the song actually started.
There was a similar, though more rare, effect with LPs. If the grooves were cut tightly spaced, the first bars of a song could be slightly modulating the "silent" lead-in groove just ahead of it. This imperfection was quite rare, and what we often heard was actually the LP's reproduction of print-through on the master tape.
On your CDs, I would guess you are hearing print-through from the master tapes. Perhaps careful engineering should have muted this out during production of the CD. Of course, you could in fact be going nuts and imagining the whole thing.
There was a similar, though more rare, effect with LPs. If the grooves were cut tightly spaced, the first bars of a song could be slightly modulating the "silent" lead-in groove just ahead of it. This imperfection was quite rare, and what we often heard was actually the LP's reproduction of print-through on the master tape.
On your CDs, I would guess you are hearing print-through from the master tapes. Perhaps careful engineering should have muted this out during production of the CD. Of course, you could in fact be going nuts and imagining the whole thing.