My bet would be that somewhere along the lines some of your speaker wires are toching. This can cause a buzzing noise like you have mentioned. If you have some spliced speaker wires make sure the ends are secured with electrical tape. Really it's a smart move to put electrical tape on the ends of all your wires. Something else is simply to make sure that all your analog cables are completely plugged in. I'm assuming your using analog as it is pretty common. Other than the wires I'm not sure, it could be lots of things. Without seeing your setup I can't really help you out anymore. Oh and the buzzing more than likely doesn't go away at higher volumes, you probably just can't hear it anymore.