If the internal speaker is still buzzing after you attach a set of external speakers, then you have to pull the internal speaker plug from the motherboard to shut it up. It sounds like you have a small circuit problem that is allowing an errant signal to get through even though you are "disabling" the internal speaker by inserting a plug in the external speaker socket. I would consider talking this problem over with your local Mac store tech. It might be covered by the waranty and you can have it repaired for free. If it isn't covered, you will have to decide how much it is worth to you to get the problem fixed. For the cheapest fix - simply pull the speaker plug and ignore everything else. If you have big bucks just laying around, go for the new Apple internal speaker. Heck, it's only money.