The 1 most common part(s) or condition(s) which cause the symptom Microwave is loud or noisy are listed below starting with the most likely. Check or test each item and watch any available videos.
RepairClinic Item # 373304 Aftermarket (Non-OEM) part
If the microwave is loud or noisy only when cooking, the magnetron tube might be defective. The magnetron uses high voltage, high current DC power to generate the microwave frequency that cooks the food. Under normal circumstances the magnetron is nearly silent. However if it is damaged or nearly burned out it can begin emitting high pitched or growling noises. It's not normally dangerous to use a microwave oven when it makes these noises, but they are an indication that the magnetron is almost dead and will need to be replaced.