What happened two weeks ago? Was the computer moved, or the cables unplugged and then plugged back in for some reason? Is it just one speaker, or both speakers? Do you have audio jacks in both the front and back of the computer?
It could be interference, the speaker cable being plugged into a different jack, the sound card/chip going bad, the speaker cable going bad, or the speaker itself going bad.
If you have audio jacks in the front and back, try switching to the other set of jacks, especially if you are currently plugged into the front jacks. The audio jacks in the back are generally a more direct connection to the sound card/chip, so there is less chance of interference or bad internal wiring in the computer.
If it is just one speaker then it is likely the speaker itself going bad, but could still be an issue with the cable. If the cable is not permanently attached to the speaker, try swapping it between the speakers, and see if the issue moves to the other speaker.
If you have recently moved the computer, or rerouted the cables, make sure you are plugged into the audio out jack, or the headphone jack. Try swapping the cable between these two jacks to see if that resolves the issue. Also, make sure the cable is not wrapped around any other cables, particularly a power cable. This can cause interference on the speaker cable.
If none of the above works, and you have access to another set of speakers, try swapping those speakers in for the set causing the noise. If you still hear the buzz, then it is most likely the sound card/chip. You can get a USB sound card for under $20 these days.