FileForums - Does anyone know why some games don't work with DC?

I have a DC that I bought it this year, in february (new), and I have some "Backups" that a a friend gave me, and some of the games don't work. They make a very strange sound. Like the head of the laser was trying to read, but it was uneable for some reason. But some other games, it works perfect. I thought it was a DC problem with some games, but I've got Shenmue, and the 1st and 3rd CD's make this strange noise, but the 2nd works perfect. Does anyone know if this is a DC problem? The funny thing is that, some CD's that don't work in my DC, works fine in other peoples DC (older ones).
If anyone can help,
Tkx.