I have the same problem and it really is frustrating. I bought a MBP (non-retina) mid 2012 from the online store and after a few days it started with this "tinking" or clicking sound, however you call it. After a few hours of online research and being much annoyed by the accompanying sound, I decided to return the product since I was in the 14 days period. This ended all too well and after I got my refund I wanted buy a new one. This time I wanted to go to the retailer store since I thought maybe while it was being delivered my old MBP could have been damaged in some way which then had caused this tinking noise. I could not be sure.
Now the drama continues: I went to the store, I bought another MBP (same model: non-retina, coincidentally mid-2012 again) went back home and put my ears -literally- next to the computer so that I could hear whether it was making any sound. Now, after a day or so, to my surprise I heard the same annoying clicking sound (a bit fainter actually than the older one), less frequently though. I was very disappointed. (no need to say). Was it my ears that deserved the quality of being so sensitive or was it these mid-2012 non-retina MBPs that had the fault? I didn't have an answer. I then surfed around a bit more to find this discussion, read about the program that was supposed to fix the clicking. Though I was a bit suspicious at first, I downloaded it and restarted. Voila! The sound went away actually.
But now I had many more questions on my mind. What if I was blocking a serious problem by making it silent for the sake of my sensitive ears? Some people claimed that this clicking could be the sign of a HDD problem, a failing drive! I wouldn't want that. There is this last thing: I did notice a few "tinks" today as well (not so frequent though). I wish I had the chance to compare with another MBP. You cannot do it with a one that is on the store because it is so noisy there, it is impossible to hear such a faint noise. But when you are alone in an empty room, it can drive you crazy! And besides, if this machine is really dead-silent like it claims itself to be, than it better be that way.
Now the question is: should I return this second MBP? I really don't want to do that but I still can since I am in the 14 day period. But I really am not the "consumer" type and could do well with this machine if it promised to work without any HDD failures in the next few years. But no one can guarantee that, can they? 😟 If I do return this, I don't think I shall buy another non-retina MBP. I do not even know whether I can buy another apple product ever again.