I have a paging problem with an NEAX 2000 IPS where phones in the far part of a plant (about 600 ft away from the IPS) sound muffled when they page. When phones page from up front closer to the IPS they sound fine. Theres only one page feed going from the IPS to an amplifier, it seems strange that there would be a difference from phone to phone. Any ideas?

Deteriorating wiring out to the far phones?

its about 2 years old. Still very new and in a room temp. climate.