I guess this started since I re-attached my back wheel after installing a new tube. After putting it on I discovered my highest gears on the cassette were unreachable, so I read up on tuning the drive train, and spent hours playing with the cable tensions until everything was honkey dorrey. But, my drive train is noisy. The gears aren't running smooth, it's like something got shorter or something got longer. The derailleur seems to squeeze the chain then let it out in a burst. Here's a video.
As I say, I don't know why. I don't think my hanger is bent:
Now, the rattling is pretty audible in a quiet garage. While riding the situation doesn't sound so dire, especially the higher the gear I go. I only noticed it today when the wind died and I was going slow enough to notice. I certainly can't feel any vibration in the gearing.