in this case the wobble was quite bad- in fact when I was cycling home I really thought the wheel was in danger of coming off. I got off at one point and checked that I hadn´t lost a spoke and was baffled to see everything looked normal. It was just when riding particularly when the cranks not moving that I noticed the chain twitching and jumping around and the only reason for that can be cassette twitching. Then when I took the wheel off I could feel that the cassette was moving way more than any normal play.