Thermal fault. Doesn't switch on properly when too cold or too warm. Makes a high-pitched whistle. Occationally works fine. Have heard others with the same model tuner struggle with the same thing, so I gather it's a design or construction flaw.
Take it back where you bought it for a refund under the Sale of Goods Act. Take evidence with you that it is an inherent fault. You have up to five years to do this in England and Wales.
T
May 2015
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