I don't know about Australia, but in the US, you are responsible if you are causing interference in somebody else's licensed band. Even if you didn't mean to, you are transmitting (noise) on a licensed frequency without a license. If it even looks like it might be because you made some modifications to radio gear, you can be liable for a large fine (and depending on the band possibly jail time).
I remember a few years ago a convenience store near Miami's airport was closed by the FCC because they had some dodgy electronics (door opener or bar-code scanner) that was interfering with the air traffic control radio frequency. The FCC forced the store to close (and IIRC shut off the power because they weren't sure of the source device) until they could prove they had non-interfering equipment.
Even the ISM (the so-called "unlicensed") bands, like 900 MHz and 2.4 GHz, are very tightly controlled. Equipment must stay within regulations on channels, power limits, and usage. Your equipment must be able to handle interference from other devices operating within the regulations, but if somebody operates outside the limits, they are liable and must shut down (and face fines, etc.).