I have static noise in the speakers and headset

Typically that noise happens when computer and speakers have different ground levels, explained here. Are you sure that you did not also change anything in that regard, different outlets, etc? Is your pc connected to other devices, antennas, network switches, etc? Try connecting your speakers and computer at the same power outlet, with an extension cord.

edit:

• When I disconnect the audio cable from the speakers, there's no noise.
• When I connect the audio cable to the speakers only (not to the computer), they are very noisy.

very odd behavior, looks like there is something wrong with the cable or the speaker system itself. Is it a hissing noise or a deep hum?

Besides eliminating interference, another suggestion:

Turn down the sound card/chipset volume from 100% to 75%.

Turn down inputs to the sound card/chipset from 100% to 75%.

Then, use the speaker's amplifier to compensate for any deficit in listening volume.

Why does this work? Amplifiers amplify, and when there is no useful sound to amplify, they will amplify noise. By turning down the sensitivity of their inputs and the volume of their outputs a bit, you'll cut the noise a lot.

In addition, it may improve your audio sound quality. When everything is set at or near 100%, a form of distortion called clipping occurs. This is when the tops and bottoms of sine-like waves get cut off flat, because they exceed the capacity of the amplifier (or sensitivity of the pre-amp inputs, etc). The result looks more like a square wave than a sine wave and sounds more like a square wave, too.