Do you have a source other than the iMac, an mp3 player or laptop, with a headphone jack you can plug the cable into? That would tell you whether the static is coming from the iMac or the cable/speakers.
If the static is still there with a different source you might move that setup to a different location to see if there's interference from something else in your computer room.
The object is to isolate the variables one at a time until you discover the problem.
If the static is still there with a different source you might move that setup to a different location to see if there's interference from something else in your computer room.
The object is to isolate the variables one at a time until you discover the problem.