My microwave is 4 years old and has worked well for an expensive microwave. I recently have been using it and while for example I warm up a cup of coffee I see sparks in my microwave. I do not have any metal in the microwave. This is happening on all things that I put into the microwave lately. I hope that this is a quick fix and not the microwave going bad. I spent over $600 and it should last more then 4 years!! Please help.