His scanner is able to pick up communication from Palmerston North, but if he comes any closer to Wellington he can no longer hear it.
When he first heard the pig noises, he thought: "Who's being that stupid? What an idiot.
"Sooner or later you'll get caught out."
If police were to catch out the oinking man, he could face up to a year in prison for criminal nuisance.
A police spokesperson said police were aware of the issue, and any interference with a police radio "constitutes a risk to public safety".
The man has also been heard performing poems, playing rap music, and singing obscene lyrics about police officers' mothers, Fairfax reported.
Holt said he hadn't heard anyone respond to the man.
"He sounds a bit drunk or a bit strange. He didn't sound like a normal sort of person."
He expected the man had a bone to pick with police, or had mental health issues.