Ok if all other sonds sound normal, you have a problem with your Magnetron/diode. These are normally warrantied for 10 years, You may want to check your owners manual for this. If it is in warranty call the number in the book and they will instruct you from there. If it is not under warranty mag/diode assy will run around $125 for the GE's and you need to know exactly what your doing to change it. Not for the average do it yourselfer. So you might want to get a new one if not under warranty. Hope this helps.