strange noise from speakers.
 

So I have a set of Altec Lansing speakers, complete with sub, hooked to my computer. Everything is great. Then I move my computer, and now there's this low thumping. Sort of like dull helicopter blades. And it isn't my soundcard, because it doesn't come through the headphones hooked through the speakers.

Any ideas?

The speakers could be resonating with something else.

I have no idea, really, but that would be my guess at least.

Check for crossed wires.

Do you have a wireless router in the room, near where the speakers are? Many DACs and even some speakers can pick up interference from wireless activity. The headphones plugged into the speakers might reject the noise because of a higher impedance or other factors.

Sometimes speakers get unhappy if they're plugged into a different outlet than whatever is providing the source.

Is the thumping present all the time or when a sound is being played (be it music, movies, games, etc)

I assume all the time but want to make sure. if it's there all the time try disconnecting it from your computer but leave the speakers on, see if it still does it. then touch the end of your speaker wire (that plugs into the pc) with your finger and see if you get anything.

another thing you can do is plug the speakers into say, an ipod, and check if the distortion is still there. Even if it's not your soundcard, the ipod could sound crystal while the computer not (for reasons unknown at this time)