I have a question about something I have just started experiencing. When there is vibrato in the voice, the larynx starts moving slightly up and down – it has never happened to me before, what is that?

The bobbing of your larynx is a sign of release. That can be good or not depending on other factors and how severe the movement is. I would say that you should never try to fix it. Think of it as a symptom and work on the overall coordination instead. Ideally the larynx should be stable and the tone steady. It is possible that what you are noticing as vibrato and the larynx moving is actually a slight instability. Observe if there are times when it doesn’t move, but don’t try to change it directly. That will cause interfering tensions and create new problems. It will change with improved coordination of the whole instrument.