Update....for the record..
The `noisy` chain has behaved itself for a few days while the weather has been crap (cool and rainy).
Today after 8 hrs standing .... sun out and indicated outside temp 18.5c.......cold start up......noisy chain back!!
Let her warm up for 5 mins then noisy went away!!..........weird !!!
May sound wierd and may not apply but does the RS3 have a vanos cam chain balancer ? I heard that few Audis suffer from Vanos rattle on start up and although only a small component it's a high labour cost job to correct