There's always a bzzz sound coming out when plugged in.

Hi i think u plug the speaker pin in wrong port,Make sure that u plug the speaker pin in green color port on front side the cpu or @ rear side of the CPU. then u should check the speaker's button and volume controller by adjusting them slightly to right and left or up and down to check the buttons working properly if the sound comes ehile adjusting the buttons the u hav to fix the speaker by mechanic.

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if there's buzzing coming out, there's probably a rip in the actual speakers. Something is torn on the inside thus the weird buzzing noise.

Unless it was a zzzzzzzzz...... noise then there's probably some sort of interference. Possibly cellphone close by, or some other magnetic thing to create that annoying sound.