Wires not connected properly, mice eating away on wires, to far from staition to station.Without being in front of the product it is hard to correctly troubleshoot.
i sold this http://www.ebay.com/itm/Panasonic-Electronic-Modular-switching-system-308-Easa-phone-model-KX-T30810-/160819364530?pt=Phone_Switching_Systems&hash=item257194c2b2 and the customer says that there is static on station 11 (which is where you program the whole thing) what could be wrong?
Have him switch phone and plug it in directly to the box (not thru wiring) if the problem persists it could be broken.
bump