Sparks coming from inside of oven body - GE Spacemaker JVM1540 Microwave Oven

proceed according. God bless youIf you see arcing or sparking inside a microwave, turn unit off immediately. Arcing can be caused by having something metal in the oven cavity touching a side, an oven shelf is touching the side of the cavity, an oven shelf support has broken, microwave waveguide, or bad magnetron.
If your microwave has a shelf in it, and you do not use it, keep it out. If one of the shelf supports breaks or comes out, the microwave will arc where the support was. You will have to sand the spot down, paint with appliance paint and re-install support. If the shelf shifts on the support and touches the side it will arc.
Your magnetron waveguide will either come out of the top, or side of the oven cavity. Some will have a stirrer in it(mostly top waveguides) with a panel over, or just a cardboard type cover over it. Over time, the stirrer cover can become warped from the heat which will expose the stirrer's metal shaft which will then cause sparking. These covers and stirrers come in a kit and can be replaced from inside the oven cavity.
Your cover over a side waveguide is coated with a substance on it, and overtime this coating can come off from the heat and moisture in the microwave. These waveguide covers are very easy to replace from inside the oven cavity. Touch up any paint that may have chipped or come off because of the arcing.
If your waveguide cover and/or stirrer are all OK, then the spark is coming from your magnetron. The antenna on your magnetrom has overheated and burned, sending the microwaves out at the wrong angle. If you catch this microwave oven repair early enough, you can usually get by with just replacing the magnetron. If the arcing has caused servere damage inside the waveguide, you will need a new microwave. Waveguides are not replaceable and most you can barely see into them, let alone sand and re-paint. In this case of microwave oven repair, when you remove the magnetron, you will see the burned antenna, or your magnetron will fail the test below.

see this steps and fix it. God bless you
If you see arcing or sparking inside a microwave, turn unit off immediately. Arcing can be caused by having something metal in the oven cavity touching a side, an oven shelf is touching the side of the cavity, an oven shelf support has broken, microwave waveguide, or bad magnetron.
If your microwave has a shelf in it, and you do not use it, keep it out. If one of the shelf supports breaks or comes out, the microwave will arc where the support was. You will have to sand the spot down, paint with appliance paint and re-install support. If the shelf shifts on the support and touches the side it will arc.
Your magnetron waveguide will either come out of the top, or side of the oven cavity. Some will have a stirrer in it(mostly top waveguides) with a panel over, or just a cardboard type cover over it. Over time, the stirrer cover can become warped from the heat which will expose the stirrer's metal shaft which will then cause sparking. These covers and stirrers come in a kit and can be replaced from inside the oven cavity.
Your cover over a side waveguide is coated with a substance on it, and overtime this coating can come off from the heat and moisture in the microwave. These waveguide covers are very easy to replace from inside the oven cavity. Touch up any paint that may have chipped or come off because of the arcing.
If your waveguide cover and/or stirrer are all OK, then the spark is coming from your magnetron. The antenna on your magnetrom has overheated and burned, sending the microwaves out at the wrong angle. If you catch this microwave oven repair early enough, you can usually get by with just replacing the magnetron. If the arcing has caused servere damage inside the waveguide, you will need a new microwave. Waveguides are not replaceable and most you can barely see into them, let alone sand and re-paint. In this case of microwave oven repair, when you remove the magnetron, you will see the burned antenna, or your magnetron will fail the test below.

see the guide for test the magenetron and another component.

see this next steps. God bless you
If you see arcing or sparking inside a microwave, turn unit off immediately. Arcing can be caused by having something metal in the oven cavity touching a side, an oven shelf is touching the side of the cavity, an oven shelf support has broken, microwave waveguide, or bad magnetron.
If your microwave has a shelf in it, and you do not use it, keep it out. If one of the shelf supports breaks or comes out, the microwave will arc where the support was. You will have to sand the spot down, paint with appliance paint and re-install support. If the shelf shifts on the support and touches the side it will arc.
Your magnetron waveguide will either come out of the top, or side of the oven cavity. Some will have a stirrer in it(mostly top waveguides) with a panel over, or just a cardboard type cover over it. Over time, the stirrer cover can become warped from the heat which will expose the stirrer's metal shaft which will then cause sparking. These covers and stirrers come in a kit and can be replaced from inside the oven cavity.
Your cover over a side waveguide is coated with a substance on it, and overtime this coating can come off from the heat and moisture in the microwave. These waveguide covers are very easy to replace from inside the oven cavity. Touch up any paint that may have chipped or come off because of the arcing.
If your waveguide cover and/or stirrer are all OK, then the spark is coming from your magnetron. The antenna on your magnetrom has overheated and burned, sending the microwaves out at the wrong angle. If you catch this microwave oven repair early enough, you can usually get by with just replacing the magnetron. If the arcing has caused servere damage inside the waveguide, you will need a new microwave. Waveguides are not replaceable and most you can barely see into them, let alone sand and re-paint. In this case of microwave oven repair, when you remove the magnetron, you will see the burned antenna, or your magnetron will fail the test below.

see the next steps and follow with common sense: God bless you
Microwave is arcing If you see arcing or sparking inside a microwave, turn unit off immediately. Arcing can be caused by having something metal in the oven cavity touching a side, an oven shelf is touching the side of the cavity, an oven shelf support has broken, microwave waveguide, or bad magnetron.
If your microwave has a shelf in it, and you do not use it, keep it out. If one of the shelf supports breaks or comes out, the microwave will arc where the support was. You will have to sand the spot down, paint with appliance paint and re-install support. If the shelf shifts on the support and touches the side it will arc.
Your magnetron waveguide will either come out of the top, or side of the oven cavity. Some will have a stirrer in it(mostly top waveguides) with a panel over, or just a cardboard type cover over it. Over time, the stirrer cover can become warped from the heat which will expose the stirrer's metal shaft which will then cause sparking. These covers and stirrers come in a kit and can be replaced from inside the oven cavity.
Your cover over a side waveguide is coated with a substance on it, and overtime this coating can come off from the heat and moisture in the microwave. These waveguide covers are very easy to replace from inside the oven cavity. Touch up any paint that may have chipped or come off because of the arcing.
If your waveguide cover and/or stirrer are all OK, then the spark is coming from your magnetron. The antenna on your magnetrom has overheated and burned, sending the microwaves out at the wrong angle. If you catch this microwave oven repair early enough, you can usually get by with just replacing the magnetron. If the arcing has caused servere damage inside the waveguide, you will need a new microwave. Waveguides are not replaceable and most you can barely see into them, let alone sand and re-paint. In this case of microwave oven repair, when you remove the magnetron, you will see the burned antenna, or your magnetron will fail the test bel

This sounds like the inner lining is coming off and alloying the metal interior to spark. You will need to repair the liner and this should fix your problem.

Remove the plate and clean it with warm water

usually sparks come from turning and cooking with nothing inside the microwave..if there is grease or something on the bottom the heat will generate a spark

The problem that you are having is that the magnetron inside the microwave is shorting out to ground and it will find the shortest path to reach whatever has metal in it. Replacing the magnetron will solve your problem altogether and you need not do anything else different and continue using your metal racks.

The cover is probably the magenetron. That is where the microwaves come from. If the bread was moist, it might have left condensate in the unit which is causing the sparking. Unplug the unit, leave the door open over night. If you can remove that cover, do so. Be sure to carefully replace it before using the unit. Never turn on a microwave with nothing in it.

check halogen light holder and connections, and any damage body, check inside body of microwave oven , because of microwaves some sparks comes from damaged body..