A MiniDisc recorder does have a laser I have the manaual for a Sony MDS-JE780 in front of me - by chance I was checking a message from the display.

On the first page there is a warning that it contains a Class 1 laser and a copy of an internal warning label that it uses invisible radiation - when open and interlocks defeated avoid exposure to beam.

Minidisc reads very similarly to CD but has a compression system (lossy recording) that allows the amount of material to be fitted into a smaller disc. I hadn't realise it uses magneto optical properties to write.


wikipedia minidisc description

This is not a great deal of help technically.

Was there any chance that the minidisc was exposed to considerable vibration while recording?