We haven't had a problem with a gty cabin. At any time (whether you booked gty or selected a cabin) if you have a noise problem with your cabin, you should let guest services know. This may be caused by a screaming baby next door (we had this once) or an "on the ship" issue....or there may be a different problem in your cabin--malfunctioning equipment or something. Guest services will either get the problem fixed or move you to another cabin. Even on a "full" ship, there are empty cabins.
We had an equipment malfunction once. Engineering tried twice (for over 2 hours each time) to fix it, then basically said that I'd have to live with it. I called Guest Services and suggested that they either needed to replace the item or move us. They moved us to another cabin of the came category. This was a cruise listed as "full."
Another time, we had a screaming baby in the next cabin. We were contacted by a CM (we did not complain on this one) and offered a move. I don't know how they knew about the problem, but.....I suggested that we give it another night and if it was still an issue, I'd let them know. I never heard the child after that.
No matter what the problem, tell GS. I don't think
DCL is deliberately not telling you what your assignment will be. Inventory changes all the time. Keeping you as gty just allows them flexibility. Besides, you can always hope for the pixie dust upgrade!