Hi Youngmic
Heres another two possible answers to your question
1. The Ceduna ADS-B station came on line (or maybe is still on test) in the last few days. Now ADS-B is not suposed to transmit on 1090, but that is a possible cause of the interfearence.
Note: The AsA map is a bit hard to read, and the ADS-B station may not be in Ceduna, but it is in that general area.
2. Someone or something is transmitting a signal on 1090. There are several possible sorces like the warship thingy.
If the signal remains stationary on your unit, i would sugest interfearance from something in your aircraft causing a false signal.
Can the unit be used outside the aircraft, if so try that and see if the signal goes away.
richo