I bought a new 15" MBP on Christmas Eve. Within minutes of using the machine it exhibited this same key noise issue for the T key. I gave it a few hours of use to see if it needed to be broken in, but I didn't feel good about waiting longer for a laptop that shouldn't have a problem like this. I returned it and they gave me a brand new one, no issues. I told them about the keyboard issue.
Now I have the replacement and it's starting to do the same thing with the B key. It's only the B key. As others have described, it seems to happen most once the machine is warm. This is why nobody can ever make it happen when they get to the Apple Store (it's been on sleep and cooled down significantly).
If this doesn't go away I'm going to take it in for service, but this definitely sounds like some kind of manufacturing defect that isn't effecting everyone. Definitely annoying for a laptop that costs this much. I love this keyboard otherwise, though