Print-through
The field from a strongly recorded layer of wound tape prints a faint ghost onto the neighbouring wrap — heard as a pre- or post-echo.
When magnetic tape sits tightly wound on a reel, wrap presses against wrap, and the field from a heavily recorded stretch slowly magnetises the thin backing of the layer next to it. The result is a muted copy of the sound that rings just before or after the original — the classic ghost on old master tapes. It gets worse with thin tape, warm storage and long stretches left untouched.
The remedies are old: re-wind the tapes periodically so the magnetisation never settles in, and store them tails-out so the ghost lands as a post-echo rather than the more distracting pre-echo. Data tapes (DAT, DDS) suffer it too, but error-correction codes sweep it away before anyone notices.