Sony Xperia Z is an awesome device with its really good hardware and resistance to water and dust. But recently a lot of people have been reporting about the back panel being loose and thus by compromising the water resistance of the device. The reports say that the back panel becomes loose and that causes the back panel to raise a little bit.
The issues seems to be happening in places with hot weather mostly. Another reason is if the phone is being used for heavy applications like high intensity games. These games/heavy tasks increase the phone temperature which then melts the glue holding the pack panel. The melting occurs where the snapdragon chipset resides.
To make it worse, Sony service centers are turning people back when people bring the phone to fix it under warranty. The reason for this is said to be “there is no way the Sony service centre employees could tell if the phone was damaged by tampering with the phone or it happened without any foul play.” Anyway by looking at the forums, people are trying to fix it by themselves. Some are using a hair dryer to melt the glue and push the back panel back in. Some people are using glue externally around the edges as a temporary measure. Let us know if something like this has happened to you by commenting below.[line]
Source: Xperia Blog