JVC AV32R25 series tv making electronic pulsing noise, please help!

I have a JVC AV32R25 series tv (the version with subwoofer inbuilt) and have recently accquired an unwanted background noise. This noise sounds as a low electronic pulse and is unafected when the volume is turned up or down. Muting the volume as well as changing the manner of output (switching from dolby to one of the alternate audio choices) is the only thing that removes the noise, however these solluitions also take away all other audio output. Has anyone any idea what is causing the noise and how best to alleviate it?

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