Many have had the same issue (I did) and it was related to a rear window seal. Some will get water behind the back seat, some will hear sloshing, and some get both. Your dealer will need to replace the entire rear window or replace the top - and ALL dealers are aware of this issue. There should be a long thread on this well known issue on this board. Search for water leak hardtop'.
Is there an official TSB Jeep has put out for this?
No TSB has been created (that I know of), but it is a well known issue for the first run JT hard tops. My dealership was dealing with multiple instances when I was in with mine. There was even a waiting list for the replacement glass to come in because of demand. The issue was explained to me as a pinched/split seal during production which required full window replacement to resolve - as the seal was fused to the window frame and there was a high likelihood of the original window being broken during removal. At one time, there was a thread here with people posting pictures and even talking about windows being broken during replacement and some dealers chipping their tops. If I find the link I'll post it here.
Crazy that would slip through QC. It may never leak, but may be better to get it replaced now under warranty.
