you should really request a return - the noise is not normal and not all rMBP have this problem - coming from experience and having had replacement units that did not exhibit the noise issue.. that said, I have been frustrated with the build consistency of these new retina macbook pros, I just sent back my 2nd replacement due to some other hardware inconsistencies and I am now requesting my 3rd;
so far when one problem has been solved another arises, (my first was making the buzzing noise noted in this thread, my second was making a even stronger buzzing noise in addition to having gaps on the bottom of the base plate assembly, my third would make loud clicks every time I opened and closed the lid as if it were catching on something internally - in addition to squeaking and cracking all over the place... now onto my fourth within 6 weeks..!) I am really hoping this to be the last time I have to deal with a replacement, its been a huge inconvenience, having had a single working laptop is what I expected from Apple.
My girlfriend has also ordered a rMBP with the same configuration as mine (2.6i7/512SSD/16GBr), I am hoping her computer fairs better, if its doesnt I am going to take this up with Apple management, its not fair to have so many issues with several brand new $3k computers.