What are the causes of rear derailleur chain noise? My rear derailleur is making some noise and I'm having trouble diagnosing the cause. It seems like it's coming from the rear cogs and sounds similar to chain noise. I'm re-building my bike after an accident, so it's possible that something was bent though I don't see any gross damage to the RD. I've spent some time browsing this site and others for ideas, and have checked the following:


Checked hangar alignment
Lubed the rear cogs
Lubed the chain
Checked the b-limit setting
Indexed the gears &amp; ensured they shift well
Checked for chain stretch (chain only has ~250 mi on it)


Can you think of any other causes for a noisy rear derailleur? I have a video if it's helpful. 

EDIT: Thanks everyone for the help and suggestions! It ended up being a combination of a bent hanger and a twisted derailleur cage. I replaced the hanger with a new one which helped to reduce the noise, but there was still some prominent noise coming from the jockey wheels, mostly on the smaller cogs, and only when in the large chainring. I changed the derailleur and the noise is now gone.
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.