He's saying shutup just for the noise?
Anyway, a 4 year old may still be seen as a nuisance by some older siblings in such a case. It will probably get better in 1-3 years. He may be concerned that his little brother is going to hurt his game or something.
Two more things. Apparantly some siblings just don't get along. ALSO, a lot of kids(I, and I guess many here are exceptions though.) listen to PEERS before themselves, and will listen to their parents only in some of the other circumstances. SO, if he listens to classmates before you, he is being normal.
I would listen to myself, and weigh the circumstances between peers and parents and other info. So my tastes in music, use of language, etc... were very different from my "peers".
As far as scareing his brother on purpose? I had an "uncle", actually just a male friend of my mother if you know what I mean, that would constantly try to scare me when I was a little kid. So I guess people might try to do that at any age. 8-(
Steve