Originally Posted by oldbobcat

Noise like this is usually caused by the chain binding or not lining up with something, like a chainring, a cassette cog, or a derailleur pulley. On some of these I've noticed a slight twist in the derailleur cage, i.e. the pulleys are not in line with the chain/centerline of the bike. To test this, first determine if it gets quieter in different gear combinations. You can also eyeball this alignment from above. Finally, you can impart a slight twist in the cage with your hand as you pedal on the stand. Do that in a gear combination that puts the cage in a vertical orientation. If that quiets it, give it a permanent gentle twist with an adjustable spanner.

Something else I've seen for which I've caught hell on this forum is the derailleur pulleys not being in line. That is, the lower (tension) pulley was cocked out because of a slight bend in the cage. Somebody tried to convince me it was normal. It isn't. If that's the case consider warrantying the derailleur against trying to straighten it yourself.

Originally Posted by 55tele

I think the most likely scenario so far is slight twist of the RD cage and / or misalignment of pulleys….