I don't know your model, it may be different to what I describe
90% of noise in my experience.
Generally, the platter sits and rotates on the ring-turn or support ring. The drive is from the centre of the turntable, however the turntable does not rest on the drive coupling, but is driven off the flanks of the drive coupling. Therefore all the weight of the platter and product goes directly on the rollers of the support ring. the support ring rollers run around the bottom of the microwave which is a big metal drum. Therefore, ANY specs of food lying on the metal base of the oven, or specs of food sticking to the drive roller surface cause the platter and rollers to flick up and down, beating the drum, making a loud noise. The wear internally on the rollers and spigot or food inside the worn rollers adds as well, and sometimes needs replacing. If the rollers wear down it can allow the platter to sit on the drive coupling, and the spigot can wear or the rollers can run untrue weaving back and forwards, or have flat spots on them.
Chipped paint on the microwave base where the rollers run, that's another set of drum sticks belting away.
Clean the bottom of the oven so it is spotless. Scrap the underside of the platter with a razor blade so there is nothing attached and wash clean.
Fine wet/dry sandpaper or scourer to each of the rollers to ensure they are perfectly clean, and ensure they are perfectly round or replace the ring.
90% of the time, the microwave behaves like a brand new one.
Turntable motor and drive coupling wear/noise makes up the rest.