It may be normal, though not owning a 360, and having no interest in games with no real plot like GTA, I can't say for sure.
My guess would be it's just a matter of how the discs were mastered for the different games. Sometimes the developers spend a lot of time optimizing the file placement on the disc(s) to minimize loading times, and other times they'll just dump all the files onto the disc any which way. Games with deliberate file placement will likely be a lot quieter since the drive doesn't need to seek so much, and games where they just dumped all the files onto the disc in a haphazard sort of way, will require more seeking and thus make for a noisier experience.
That would be my guess anyway, even though I can't say as I really have all that much to back it up. But I would say that so long as it only seems to be specific games, and not all games, it's more likely normal than abnormal.
I know on my old PS2, the game Tales of the Abyss really grinds away at the drive, while most other games you can't really hear the drive over the cooling fan.
i have noticed on my xbox when playing gta4 and gears of war i can hear the disk being acessed in the disk drive it is quite noisy, on halo 3 and oblivion i can hear nothing it makes no noise its not that bothering i was just wondering if anyone else knows if its suppose to be that noisy as long as it is normal i don't care about the noise could anyone help me with this its about as loud as my pc acessing a disk but would be so relived if anyone could confirm if there disk drive is quite noisy when acessing the disk and if possible explain why it is noiser on some games more than others