I'm assuming this is a new computer and it's not something that changed after a while (which would point to a hardware issue).
If this is what happens:
Insert disc, the drive grabs it, then it goes "Whirr, click, click-CHUNK, buzz" (or something to that effect) pretty much immediately, then yes, that's perfectly normal for any slot-loading optical drive. That sound is, I assume, the drive locking the disc onto the hub before spinning it up.
If you mean you put the disc in, and then a few seconds later it starts making funny clunking sounds, then no, probably not normal.
If you're really worried you can always call Apple and have them listen over the phone--it's free for the first 90 days even if you didn't buy AppleCare yet.