High pitched sound being made by sub-woofer

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My computer speaker system sub-woofer is making a high pitched sound. This just started a week or so ago. Besides being very annoying even though it is not super loud, I worry about what it will do to my hearing since at my age it might even be considered surprising that I can still hear that high a pitch. So I don't want the constant hearing it to damage my hearing. Unfortunately in my crowded "office" it is not easy to get to where I put the speaker back before I added something to the office. So I don't want to go to all the trouble to get to it without having some kind of plan to solve the problem. Some suggestions or a link to a site on such things would be helpful.