Sparks and strange noise when microwave is turned on even when empty inside. i have a ge jvm1850smss over the oven microwave.

How to Fix Microwave Oven Simple Fuse Replacement
be careful microwaves hold power and can zap you

There is a separate fuse for the magnetron. Usually inside the case. The magnetron is the part that makes microwaves. The door switch could also be the culprit.

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.

The fan is for air circulation regulation, e.g. preventing steam (and smoke) from building up inside, and also stops air pressure from building up inside so you won't get a blast of steam coming out or worse. On the convection side it heats the food faster and more evenly. You will need to replace the fan assembly to keep the microwave safe. the noise and sparks are probably due to spent bearings and / or a dislodged fan scraping against another surface or something getting in the way of the fan

One of the door switches is probably defective, replacement only option.

Presuming that you have iliminated the possibility of any metal objects that are not meant to be in the machine being in there (and this includes dishes and other items with silver or gold leaf on them, which WILL spark and burn!) then take a look inside the oven its self. You will find a waveguide cover. It is usually a strange flakey silvery plastic/card like material called Mica and is usually on the same side of the microwave wall as the control panel (So if the picture on this thread is accurate, I will guess the Mica cover is on the right hand wall inside as you look at the machine from the front) . Over time, the magnatron (the thing that creates the microwave energy) will often burn a hole through the mika, or cause a dark brown or black burn mark in it. If this cover is even slightly damaged then it may well cause sparking inside the machine. These covers are designed to be removed and you can buy replacements for them from electrical stores.

sounds like its shorting out,dont recommend trying to use,could start fire

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

You need to have the capacitor and Both HVdiodes replaced. Suggest a technician do it . Dangerous voltages present even though off.

remove the round button(s) and remove the cover..clean thoroughly and replace anything thats burnt, if metal clean and paint touchup