Yep, I have this issue on my late 2013 15" MacBook Pro Retina.
Apples customer support has been absolutely horrible. There are no Apple Stores in Denmark, so repairs go through certified thirdparties. I bought it in to a certified service center (called Eplehuset) for the first time in January 2014.
Here is a video of the problem before handing it in for 1st service: https://www.youtube.com/watch?v=LB5m9wqQpgk
(only light pressure is applied, the sound comes when you rest your wrists so it's pretty annoying to listen to everytime you use the machine)
Eplehuset claimed that the problem was caused by the top case, and they replaced it. Actually, the service report reads "the topcase now obeys to Apple's specifications". Hold it there one second: the certified service center claims that my original brand new unit came with a top case that did not obey to Apple's own specifications - hmm, that's strange.
I hoped the problem had been solved, but it didn't take long to realize that it hadn't.
I took these two videos after the top case had been replaced:
https://www.youtube.com/watch?v=GPzW4KqAZSA
https://www.youtube.com/watch?v=MZMhOak4d0s
Oh well, called Apple again, and they said I would have to turn it in for service once more. This time I chose a different certified service partner (PC Service Center) as they had less estimated repair time. The technichian identified the bottom case to be the cause of the issue. In his report, he writes that the bottom case is bumpy/uneven. This must be on the inside as it seems plain on the outside, and hence it must have been there from when I got the computer. Anyway, in order to be able to replace it, the technichian must first call Apple to get authorization. Apple declined claiming it was "not a hardware issue" - well if the case is not part of the hardware, then what is the case then? Morever, the computer got a tiny scratch on the alu-back of the screen from this visit to the service center. I chose not to do anything about it at this point as this service center had been really nice to me (e.g. not charging comission for looking at the computer), especially compared to the treatment I've gotten directly from Apple up to this point.
Called Apple again informing them I could not understand how a defect that the computer had shipped with was not covered by the warranty. They claimed they couldn't do anything but send me back to Eplehuset. I revisited Eplehuset, and the technichian simply took the laptop appart and cleaned the inside - claiming that this solved the issue. Didn't take me more than 5-10 minutes of use to see that it didn't solve it.
Called Apple again informing them that now I've had it and wanted a replacement machine (after all, I've had it in for service 3 times now). They refuse to replace it claiming that they can only see the first service (the top case replacement) in their systems. Emailed Apple service documents from the two other "repairs". Tomorrow they are going to call me to inform if they'll replace it as it have been in for service three times. The AppleCare employee informed me today that is unlikely as it have not been "repaired" three times - it's only been looked at two of the three service visits.