What are the causes of rear derailleur chain noise?
Check for hair, grit, etc caught up in the derailleur wheels; most likely the guide pulley wheel; remove both wheels: attach the tension wheel last after cleaning/oiling.
Make sure you pay attention to which wheels go where; and the direction arrow on the tension wheel. A google search will show you a diagram of both wheels labelled and the turning direction of both wheels. eg. guide wheel is the largest wheel located nearest to the cassette. Both wheels should have labels `etched' on them.