I haven't spent a whole lot of time with my new rMBP but one thing that I do notice is that occasionally I'm hearing what sounds like a "pop" or "tick" noise, even if it is just sitting there on my desk. It's not loud but it's obviously noticeable. With no moving parts other than the fans (this is not a fan noise) I'm wondering what this could be. I'm thinking it might be from expansion/contraction or warping from the case. I guess I'm not overly concerned but it is odd since my previous MBPs didn't do this. Anyone else notice this?