Xbee S2 TX sends out 0xFF, what would be the case of that?

I have a Xbee S2 module that is constantly sending 0XFF to my MC, every ~5 seconds. I would like to know why I am getting that byte and how to stop it. I have solved that issue by ignoring any transmission until I see the start byte 0X7E. However, it wakes up my MC when I want it to stay in sleep mode. The system runs on battery.

Thanks

I am not aware of any reason why it would send out an 0xFF value unless you have the V+ command set with a value.