Frigidaire Model# GLMV168KS2 Microwave is noisy!. Unit still heats fine but when cooking it has recently begun to make a noisy rattling sound. It is not the turntable because I can turn that off an it is still noisy. It sounds like the noise is coming from above the cooking area. Once again, everything works fine except for noise factor. Is there a part I can replace before it wears out or has some ill effect? Unit is about 6 years old. Respectfully Submitted, Dave