you might be living in a dodgie area.:(
I went O/S for a while and left one car at mum and dads and another with a friend in the country. The one in the country was about half the premium of what it was at my place with the same insurer. The one at mum and dad's went up by about 50% while at a suburb only 10km away.
Crime and accident statistics by postcode make all the difference.

