Is it the sound card or the speakers?

I came home this morning to discover this horrible, extremely loud feedback-like noise emitting from my harman/kardon computer speakers (I could hear it in the garage, it was so loud). Everything was fine when I left for work last night. Rebooted, but the problem remains. I don't have another set of speakers handy, unfortunately, so I'm hoping one of the techies out there can tell me what to troubleshoot next.

Update: Headphones plugged into the front port are working great -- sound card is definitely OK, then?

 

I dont think it's the sound card if the headphones work good up front. unplug the speakers from the back and try plugging to the front jack to see if you are still getting feedback.
also,
Double check to make sure that there isnt a microphone plugged in and is on, and if it is on; make sure the "boost" feature (if applicable) isnt enabled and pointing at the speakers. this will cause horrible feedback. thats the only thing I can thing of.

 

What "front port" did you plug the headphones into? Front port of the computer, or of the speaker (ie. a bypass)?

I've found often that electronic devices near the speakers cause horrid feedback, especially powerful cell phones (like Motorolas).

Try removing the speakers form the sound card jack int he back of your computer and plugging in earphones there, see if you still get the bad feedback.

Are your speakers powered? Could there be a problem with the power cord?

 

Thanks for all the suggestions, guys -- now I know it's definitely the speakers. Even when completely disconnected from the computer, the noise persists. I already have a new set on the way from Amazon.