Unplug the oven.
Remove the glass turntable from the oven and wash it with dish soap and water using a scrub brush.
Remove the turntable guide from the oven and soak it in hot soapy water for 15 minutes. Scrub the wheels with the scrub brush until cleaned of all food debris.
Wipe the oven floor of the microwave with a soapy rag to remove all food debris. Allow the turntable, the guide and the microwave floor to dry.
Replace the guide and glass turntable. Plug the microwave in. The next time you use it, listen for squeaking. If squeaking persists, seek professional help.