Self-powered speakers, like all electronics, are subject to ground loops and interference. In the case of powered speakers, this can manifest itself as buzzing or humming. Changing the grounding scheme with powered speakers and other equipment can be a major step in solving the issue. In addition, the relationship between which outlets the speakers are plugged into versus the remainder of the gear should be addressed. In any case, solving ground loops with powered speakers to eliminate buzz, although possibly frustrating, is worth the time.
Turn off the powered speakers and any connected equipment. You will only turn them back on after each step has been completed to test for continual buzzing.
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Plug the speakers into a different outlet than the rest of the gear. Use an extension cord and/or power strip if necessary.
Flip over any nonpolarized power cords on either the speakers or the equipment. This must be done one component or speaker at a time to find the ground loop culprit. Focus on the receiver or preamplifier first.
Plug the incoming satellite or cable feed into a ground loop isolator, then onto the display or cable box. Cable feeds are often sources of ground loops.
Swap each RCA and interconnect with a replacement. Do so one by one, testing each time by turning on the speakers and system, to determine if the buzz persists.
Call a licensed electrician to check the AC panel for faulty grounding associated with the room where the speakers are displayed. Having the electrician wire a new outlet with an isolated ground should fix the problem permanently.
Test the efficacy of each troubleshooting technique after each step prior to moving to the next one. Normally, buzzing will manifest itself with or without a signal. Therefore, just turning on the speakers will let you know if the technique improved the situation.
Following all troubleshooting steps, including replacing/installing a new outlet, should solve the problem. If not, the speaker(s) or a component in the system might need repair.
Do not use "cheater" plugs. These devices lack the required grounding prong, potentially placing AC voltage at the chassis of a piece of equipment in case of a fault.