Hi, I have this microwave for about an year, it was working fine until today. 20 mins after I heat up my dinner it started beeping. (the same beeping as if you forget your food inside after use). The beeping started slow, then it became very frequent. I unplug the power for about 30 mins and then try to plug it back, but the fast beeping starts as soon as it gets plug in. Is there anything I can do to stop the beeping? Is it still save to use it? Should I unplug it when i am not in the house?