I have a single MLX-10D unit that is not working in two-way voice intercom conversations. The unit is set with HFAI on, but when the unit is paged over voice intercom, the paging party cannot hear the response over the mic. The paged party can hear the paging party over the speaker just fine. The ring intercom function works just fine. Is there some special setting to be checked for this? I checked all of the Voice Announce functions, and it is identical to all of the other phones. Any help is appreciated.