Microwave turntable noise

[Thorning]

I have a Whirlpool microwave which is a model MH1170XSB-3 . This is the type that is mounted above the stove and works well even though this unit is14 years old except it has started to make a slight rumbling noise  that is coming from the turntable . I can operate it w/o the turntable turned on and of course there is no noise. The plastic coupler was removed and checked for damage and none was found.  I can see no obvious damage in the glass turntable area and hesitate to dismantle any further and am looking for advice as to whether it is practical to remove this unit and try to repair or if it would be better to replace the entire unit since new ones are fairly inexpensive. Removal of this type of unit from its mount is a 2 man job !!!

[100 td]

Does it make noise with the glass platter removed when in rotate mode?

[Thorning]

No noise when the glass turntable is removed.

[100 td]

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.
YMMV

[Thorning]

Thanks for the suggestions. I will check all the areas you mention and see what happens.

[Thorning]

Cleaned up the surfaces  of both the platter  and the roller path and retried the unit but it did not improve. In fact it got a little louder but that is hard to quantify. I will keep checking for other causes but will probably replace the entire unit  if I dont find a real cause.

[Thorning]

I borrowed a neighbors platter and rotating support and tried it in my microwave after cleaning it . It made a difference to the noise  so I took my original parts and cleaned them even more than I did previously and cleaned the metal track area in the bottom of the microwave even more and it seems to work better than before  in terms of less noise. I would not have thought it would make that much difference but apparently is did. The amount of material removed was miniscule.