Why does my Doro PhoneEasy 610 causes loud buzzing in recipient's phone?

When I use my My Phone Easy 610 to call someone they get a very loud buzzing at their end making it almost impossible for them to hear me.  Otherwise seems to work ok.  Any solution to this problem?  Phone is nearly new and hardly used - has done this from the start.  My Vodafone SIM works ok in my old Nokia. 

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