Line Conditioner

OK, so I have a portable XM radio, and when I hook it up for power through the supplied cigarett lighter adapter I get this horrible whine that gets louder as the RPM's get faster. I would imagine coming from the alternator. I know that i could probably fix this with a grounding kit, however just wondering if anyone know of a plug in line conditioner to help with the whine. thanks yall!!
 
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