I agree that problem solving is part of Amateur Radio, especially dealing with BCI. However, as the designer and kit provider, I should have made it clear that this is something new and people may meet problems.
Perhaps it is good idea to find the source of the interference first. I did a web search and found the following stations in Hobart, Tasmania very near you:
ABC Radio 936kHz
ABC RN 585kHz
ABC News on Radio 747kHz
Compare with an AM radio receiver and you will find out the possible source of interference. If you are not sure about the finding, perhaps you can contact ABC to know the frequency list and distance of the interference, including LW, MW and SW, so you can insert a band stop or other type of filter.
Personally I have a similar experience to identify a strong BCI and finally found the source of the noise. It is a lot of fun indeed and it is good for you as you can start to try many more kits of direction conversion type later.
I appreciate all the feedback and I think it is part of the experience of providing the kit. Let me know if you need me to ship the missing part. As I am getting 42, I start to forget something. If you need me to refund to cover the postage and cost of sourcing locally, I will be glad to do so. A happy customer is more important, always.