Of course the branch makes a sound, if your saying it's a matter of perception, and you have to see it to hear it, then does it even break. If there's no one there to see it then how do we know it's broken at all?? The whole world could be an illusion it which case, you are an illusion. Unless you take Descartes' cogito but then you have the problem of 'I'. What is 'I'. It implies human existance, if there is I then there must be He, She, They. This wouldnt make sense in an Idealist view, which i presume is what your getting at with the 'does anyone hear it?'. Also with the cogito, what am 'i' 'thinking'??
you could always go along with Berkeley and have an Idealist theory of perception. i.e. 'God is in the quad' or Mill's Phenominalism, completing it and saying that things exist when they are able to be percieved. The branch breaking is able to be heard (from mill's viewpoint, and mine) so it does make a sound.
I have my philosophy exam in 2 weeks