I have a GE Profile Spacemaker Microwave oven model number JVM 1490BD, made in 2002.
Recently it has been making a grinding sound lately when the door is closed. It stops as soon as the door is open. It is not coming from the spinning glass tray. It seems to come from the upper right. I think I remember seeing a fan back in there but it appeared to be turning. The microwave cooks food still, but I believe it is cooking hotter than normal. Perhaps there is a fan that draws heat/steam out of the unit? It has revereted from a continual problem to an intermittent problem, but I want to fix it.

Also, I am not sure if it is related, but it doesnt seem to draw smoke and such from the stovetop like it use to. (This started happening way before the grinding noise). It has vent fans on the bottom that are supposed to suck the smoke up and send it through the vent out the roof. If I cook bacon on the stove, the kitchen smokes up even with the vent fans on high. I placed a small piece of toilet tissue to see if it was sucked against the fan grate, it has only a slight pull. This is supposed to have a charcoal mesh filter, but when I check to see if they were clogged, I saw no filter. I was going to get around and check the exhaust pipe on the roof and make sure it is not clogged with a squirrel's nest or something.

Thanks Gene, those links are very helpful.
Looks like the motor is part #1422. What do I look for exactly, a certain voltage on it, or that it turns smoothly? I am pretty sure it turns the fan #1421, at least it did one time when it was making that noise.