So.....
Car has been into Nissan today - technician came out on test drive and acknowledged the issue. Free of charge vehicle check done and no other faults found. Alternator / tensioner / belt adjusted apparently - now noise was initially there when i left garage, however 30 miles later and not hearing anything.....
Due a service in January / 4000 miles time so if it is still doing it then will mentioned it - at least now logged on system and fingers crossed i wont hear anything soon !