Where to find the complete manual for your Westinghouse microwave oven

My Westinghouse microwave has started making a strange buzzing sound when heating, and it’s got me a bit worried. It still works fine, but I don’t want to wait until it completely stops before figuring it out. I’ve done the basic cleaning inside and checked the plug, but I’m not sure what else to try. How do you usually handle small issues like this before they turn into bigger problems?