I got my Zaon XRX PCAS test flight

I received mine about a week ago but I haven't had a chance to fly with
it yet, so I was interested to read about it's performance in-flight.
Interesting how when it's turned on, the arrays inside the unit whirl
and revolve, obviously to point the directional antennas in as many
directions as possible to detect interrogations. According to Zaon's
website, they are going to release a panel installation. I'm sure this
will require external antennas. They'll give the unit a better view of
threats behind your metal aircraft.

Also included are interface options to output traffic data via RS-232
to AnywhereMap or True Flight.

The True Flight system is a seperate display which shows higher
resolution quadrant direction, has flight path tracking, altitude trend
and a transponder altitude monitor.

http://www.aviationsafety.com/traffic_alert1.htm

I am amazed at the tiny size of the unit, it's smaller overall than the
previous model VRX even with the antenna enclosure on top. It is, as
you say, a better alternative to Mode S. Also ADS-B Out will only
provide more traffic information to ATC. Fully operational ADS-B In,
when implemented would obviously provide the highest level of traffic
awareness to the pilot.

The XRX provides a lot of this information right now for a fraction of
the cost of TCAS and current implementations of ADS-B.

ADS-B Out will only provide more traffic information to ATC.
Also to the a/c with ADS-B UAT receiver installed. ADS-B UAT receiver
does not need ground station to receive other ADS-B Out
transmission....but the price is very high now however, the price can
be reduced dramatically since UAT is almost functional equavelent to a
now-a-day all inclusive cellphone...with a GPS, a transceiver and color
LCD display. I have seem a demo Capston system display live traffics
in Alaska in a notebook 2 years ago. It can be implemented very
easily.

the arrays inside the unit whirl and revolve,
I think the 4 directional antennas are fixed. The sound you heard was
the heat sink fan that disburses the heat generated from the CPU
chipset to its case.