When I used one, it was in a vehicle. I used to install car stereos back in the day and never had any trouble until one day when I was putting one in my own car. There was a hum I couldn't get rid of no matter what I did or tried between the head unit and main amp. Then a friend suggested an isolator and voila, problem solved.
In your case, the wireless component opens the system to all manner of interference but, if there happens to be an imbalance on your source side, this might just solve it. They don't cost much so you won't be hurting too much if it doesn't happen to work for your problem.
Thinking about it a bit more after re-reading your post; is the buzz still there if you unplug the transmitter? If yes then your problem is definitely in the receiver(s). Have you tried plugging the receivers into a different power outlet? Maybe try an extension cord if there isn't one close enough?
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