He probably can't return it, it's second hand!
It will be the power transformer, more than likely a laminated steel transformer, that is mechanically vibrating with the AC power. It's possible you could get inside (unplug it first!) and if the transformer has bolts holding it together, you might be able to tighten these and the noise should reduce. Failing that, a tech could swap it out with a toroidal type, which will not vibrate.
Hope this is of some help.
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Last edited by Tim Farrant; 31st January 2007 at 06:53 AM..
Reason: typos tpyos sytpo