Cheers for all the replies. Fairly sure that its the CV joint - been doing a lot reading on this and other forums (don't be mad - I chose this one ).
It is a very metallic ping - not unlike a good connection with a metal golf driver for those who like to follow the instructions on their boot lid.
Hoping to get the work done under a third party warranty provided by the (not nissan) dealer from where I bought the car, but need to source parts cheap as possible as they are grumbling about the cost of the parts from Nissan.
The mechanic I use is very experienced (though not necessarily with the Z, more usually Mercs) and so diagnosis should be spot on. Shown him the TSB and and the noise and he concurred that CV was at fault.
I need to PM but I'm told I'll need to make 5 posts first... Hope this isn't breaking any rules...