HIDDEN FILES CREATED BY MAC OSX
There are a few tricky problems using Mac OSX to manage FAT32 drives, including SanDisk devices.
Take a look at this webpage for a description of the problem of “Hidden Files”.
I use the software “HiM” to remove the “hidden files” created by my MacMini while copying new files to my SanDisk Clip Sport.
https://www.macupdate.com/app/mac/52076/him
FOLDER ART USING A MAC
I have been using “mp3tag” sofware on my PC and Mac to manage my mp3 collection.
Take a look at the main website for mp3tag.
http://www.mp3tag.de/en/index.html
Then take a look at the version of mp3tag modified for OSX using “Wine Bottler”
http://www.mp3tag.de/en/mac-osx.html
Using mp3tag software on my Mac, I can easily manage ID3 tags including embedded album art.
I like to use jpg files that are approx 250 x 250 pixels at 72 dpi.
Instead of embedding album art you can place a file named “folder.jpg” in the same folder as the mp3 files on your SanDisk player.