On Tue, 08 Jan 2008 00:09:36 +1300, cliff wright
wrote:

Any ideas welcome!

Get yourself a portable VHF radio that receives AM and use a handheld
Yagi to trace down the noise. Powerline interference is much easier to
DF at VHF. Pull the main breaker on your house to make sure the noise
isn't being generated within your residence. Here in the USA, the
power companies are obligated to eliminate interference emanating from
their equipment, but don't know about ZL. It never hurts to ask. The
power companies up here have very skilled folks who track down
powerline interference complaints.

Good luck with finding the source.

S.T.W.