meta data changing on its own.

I produce several radio programs. I have two music libraries on two separate external hard drives. a 1T Toshiba and a WD My Book 3T, roughly about 800 G on each of music files. I bought a new HP slimeline before Christmas and when I connected the hard drives to the new computer I hard an access issue with the 3T drive. (I posted it here) It was an sharing/access thing. That was resolved. However, all the metadata on my music files was changed. All titles, artists, years track # was erased and the Album titles were all changed to "Now, That's What I Call Christmas Music". But it gets stranger. In the course of replacing the missing and incorrect metadata (Since xmas) I have discovered that now the other hard drive music data is changing. Not all of it like the other drive, but perhaps on song in an album or one album among many of an artist. and yes the new changes are still "Now That's What I Call Christmas Music".

Any ideas?

Cue Twilight Zone theme

 

Nobody has any ideas?