I have a DME555XE1 combination microwave. There was some sparking behind the upper wave guide and the oven was making a loud "grinding" noise. I replaced the wave guides but the grinding noise remains and the microwave is not heating/cooking. Any suggestions?

dont use the microwave until you retrieve what dropped inside when you removed the port. The grinding is most likely a foreign object that is hitting the moving parts of the microwave and causing sparking. It can catch fire

Microwaves use a magnetron to generate microwave energy and direct it a rotating blade wheel to spread them around the inside of the oven. If there is any metal in the area to be heated, or any of the blades are bent, even a bit, the microwave energy can be reflected back up to the magnetron area. In this area there is now too much power and it sparks away, so it does not heat the item in the oven.
Because it is sparking it is now a safety hazard the sparks may melt and set fire to plastic parts in it. This is serious it could burn your house down. Bin this microwave and cut the cable off it to make sure no one else ever uses it.

A dirty or damaged wave guide cover can cause sparks, fire and noises. You can order a replacement wave guide cover from many appliance parts websites for less than $15 in many cases. It should fix the problem.

look for dirt inside the cavity or the wave guide cover it's arcing... make sure you have something in the microwave, don't run it empty

The wave guide could be dirty or damaged. Dirty oven interior can also cause sparking. The wave guide is probably not dirty if it's not on the interior of the oven . Some are behind the interior wall .

Our JE1860SH was also sparking after a few seconds. The GE tech pulled the upper round disk and found the problem. The plastic was burned and the round metal which is behind the plastic dome was arching with the frame. Lasted seven years expected more especially from a GE product. So my suggestion is to remove the dome and check it out.

I cleaned the microwave really well. I used a screwdriver to pull the plastic cover out enough to clean behind the edges with a soft toothbrush. Seems to have corrected the problem.

Quite often this is due to grease or food particles stuck somewhere in the cavity of the oven or stuck on or behind the waveguide cover.

They are often held in place by a plastic rivet.

It can be fragile, and the metal edges of the oven behind it can be sharp, so be careful!

The cover and the metal behind it should be cleaned with a mild, non-ammonia cleaner.

If the cavity metal of the oven is chipped or charred, it will have to be sanded smooth and clean and dried thoroughly.

Then you can apply some high-temperature appliance paint, available from places like Wal-Mart, Lowe's or Builder's Square.

If your waveguide cover is burned, it will need to be replaced. It provides important protection for the magnetron.

You can find helpful exploded view diagrams and order parts by entering your full model number from the tag on the oven here.

We're happy to help you with free advice and we'd appreciate your thoughtful rating of our answer.

The antenna on the magnetron is wearing out becuase it is damaged. Replacing the antenna from another magnetron normally solves his problem.

Your problem is due to the "magnetron" arcing to the wave guide within the microwave. Picture someone arc-welding stuff together inside the microwave casing, that's essentially what's happening. It is a fire hazard and you should stop using the microwave immediately. As far as I know, there isn't a recall on that particular model (though there was on another similar Kenmore/Whirlpool model) so if it's out of warranty, you're out of luck.