Why does the fan on your mac book makes a semi loud clicking or mooing noise when you try and play a DVD or CD?

Without seeing the machine in person, its impossible for me to tell, but if its only doing this when you play DVDs or CDs then its probably the DVD drive that's making the noise.

Optical drives spin at very high speeds when theyre reading & writing, if the disk or the moving parts of the drive are out of balance, it can make the drive vibrate & it can be quite noisy.

Note that it is not uncommon for cheaper media (like stuff you find in the $5 bin at Walmart) to do this, but if all discs are doing this, youll need to replace your DVD drive.

If that's the case, contact Apple & see if theyre willing to do a warranty replacement, the worst they can do is say no.