songs in my Music library skip - like a scratched CD would

Hi all,

Would really appreciate some help with this. Have tried various things to no avail.

I have a giant music library I keep on an external drive. I've got thousands of CDs and files uploaded in there from 20+ years of listening / learning / studying. I do not subscribe to Apple Music. I just use Music to access my library of songs.

When I play short tracks -- tracks under 10 seconds, say (which I do for ear training work and various other quizzes for my musicianship) -- the tracks start fine but then skip ahead, as if there was a scratch on a CD.

I can verify that there never was a scratch on any of these CDs -- because back when iTunes was iTunes -- all these tracks played perfectly. A lot of these short tracks were imported as files, meaning they never were burned from a CD.

Basically, this never used to happen and now it is.

One note: when I play the same tracks off my iPhone, this doesn't happen.

I've called Apple Support and one thing we tried worked ONCE -- which was switching the USB port that my external drive was using to connect to my Mac Mini.

The drive I'm using is a Glyph SSD 4TB drive. It has about 2TB of space on it still. It connects to the Mac Mini via USB-C.

I'm running Big Sur, 11.7.3 right now.

Any ideas?

THANKS so much in advance for your help.