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OH yes reread your post. XPDF is for standard lights only as it also dims. No motors or low voltage lights should be used.
Ah. SR227 good choice.You still may have a marginal signal where the problem light is. Did the filter on the problem aquarium light help at all?
Is the lights noise so bad the filter didn't help or is the filter not there yet on the lights AC Power Cord?
Get yourself an XPPF Plug in Noise Filer and plug the filter into it. Your lights will work.
Then you need to do further testing. There's something else causing noise, and one or more additional XPPFs will be needed.