Thank you for the response! Here is an update: Things seem to have improved somewhat. I am now able to execute the action "Say hi" without screaming servos, Bittle now sometimes even walks OK, but not always. Moving individual servos slowly with the Skill Composer seems fine, so it seems to be an issue related to fast servo movements, which can also be seen in the trotting video below, which is worse than walking.
This is what walking with some issues now looks like:
And here is trotting:
Looks like it might be an issue with the left front leg?