I don't know anything about that particular system, but if you hear repeated keyups on a voted conventional system, it is often either a problem with the haul-back medium (e.g., phone lines, fiber optics) or with the comparator receiver card. If the dispatchers become aware of the problem, they should simply disable that receiver until a tech can get on scene.
(What happens, typically, is something like this. Assuming a voted system using a multiplexed haul back in which the channel bank become intermittent on one channel.
(Normally, when a receiver in a voted system is squelched, it sends a 2175 Hz tone down the audio line to the comparator receiver card. This tone signals: "I am squelched; line is good." Now the haul-back dies. When the channel card loses the 2175 tone, it interprets this to mean that the receiver has unsquelched on valid freq and tone, and it responds by keying up the transmitter and gating audio (in this case, white noise) to the transmitter. At the same time, the voter starts a "voice detection" scanner; if it does not detect audio fluctuations consistent with human voice before the voice detection timer expires, the voter concludes that either the receiver or the haul-back has failed and it releases the transmitter, ungates the audio, and puts that receiver card in "failed" mode. The card will stay in failed mode until it again sees the 2175 idle tone.
(If the haul-back is intermittent, the unsquelch and transmit/ungate and faulted/fault reset cycle will keep happening until either the operator puts that receiver in manual faulted status or the tech restores the haul-back failure.)
If you hear multiple keyups on a conventional system using MDC signalling and you hear the MDC sqawk, that could mean that a subscriber has (probably inadvertently) pressed his emergency button and, for some reason, the console has not sent an MDC acknowledgement. Normally I'd expect to hear the dispatchers contacting the unit in question to inquire his status and, if necessary coach him to reset his emergency function.
