Could be any number of reasons. Digital noise is from the noise correction algorithm, trying to interpret missing data that wasn’t written in the first place, or is written incorrectly a
A tape that sheds its magnetic medium and is missing the data will give the same digital noise
if you have a master tape and it’s not read correctly, that “corrected” digital noise will be recorded cleanly and reproducably to the new copy, and will not go thru additional algorithm nor show errors on playback, as it a “correct” copy of the digital trash the last deck fed it.