"Just scanning the repeaters, and the scanner got stuck on VK3RHF at about 20:30 tonight (Tues 20th).  The interfering signal appears to have voice on it, with a somewhat echoed quality, almost like feedback between 2 SSB radios on slightly different frequencies.  Speech appears to be that of a female, but it's too unclear to interpret.

One station reported he could just hear something on the 70cm input (433.750), no one else heard anything.

If you're receiving this and it looks new, might be worth investigating..."

And later.....

"Hmm, the audio's rapidly becoming clearer, sounds almost like a phone conversation between two teenage girls or young women.  As it seems to retrigger the repeater after a time out, possibly an intermod of some sort?"

"Anyway, to finish the story, Steve, VK3USR arrived at the repeater site just as the interference stopped (and it didn't return), which left
conclusions a little up in the air."

"Some people believed the interference was the result of a LIPD, possibly deliberate interference (433.750 required tone access and the DSE LIPD covers this CTCSS frequency), because of the signal's cessation upon the arrival of someone at the site, and the signs of audio feedback on the signal, as though whoever was transmitting it was monitoring one of the repeater's outputs."

"Other than one station hearing something on the 70cm input which was barely audible, there is no evidence as to the real source of the
signal, and blaming LIPDs may be a little premature at this stage, though they remain one of the likely culprits.  Perhaps we'll never
know..."

Some extra comments...

The following day, some short conversations in another language were also breifly heard. This repeater is also linked to a 10 Metre FM repeater. I doubt if any LIPD users are allowed to operate there! Although the repeater is on a mountain top, there are still plenty of houses nearby.