Change in SuperDrive noise

I'm used to hearing noise (for a second or two) from the cd/dvd player when I switch on my MacBook or wake it after sleeping. I've had my computer for about a year, and a couple of days ago that noise started sounding different all of a sudden: a little bit weaker, slower, and lower in pitch, as if the player was struggling a little bit (the noise is still similar, but noticeably different). This started right after I used the SuperDrive to watch a dvd for the first time (I had used it for music before). I've since tried to play another dvd, and it seemed to work just fine.

Basically I'm wondering what might have caused the change, and whether there's now something wrong with the SuperDrive. Anyone have any ideas?

Thanks very much,