Hello Immie,
My first guess is he perceives your hand in his cage as a threat. His cage is his security, domain, and to him, is a sacred place. Lots of birds, including one of my own, hates me to stick my hand in the cage, but he does not panic or such, just glares at me and tries to get out of the way.
What was the position of his crest when this was going on? Up, partialy up, all the way down, or somewhere in between? Cockatiels have a definite set(s) of body language, and you can tell a lot about their current mental state by observing some subtle, and not so subtle things like body position, tail, head shaking, etc. Sometimes, they will run back and forth at the bottom of the cage, which in my case, means they want, or are begging for attention and want me to take them. Other times, they are agitated, and want to be left alone. Google for cockatiel behavior or body language, and I think you'll find quite a few pages. Here's one of the good ones
http://www.cockatielcottage.net/questions4.html
One last thing, as bird hearing is very sensitive, it could be the music is too loud. This sometimes will trigger behavior as you mention, and the bird is wanting to get away from the loud noise.
Sam












