Fan makes a terrible rattling noise - GE Microwave Ovens

This noise may be due to turn table motor or due to cooling fan confirm by checking thoroughly both the components,if it is turn table motor than only replacement is solution,in the case of fan, clean and put some oil to rectify.

If its shakeing and makes that sound , it over heated

All microwaves make some noise when running. Cooling fans, exhaust fans, turntable motor, transformer, and magnetron all make noise. I assume you mean some unusual noise. I need to know more about what kind of noise it is - a loud roar, a rattling sound, a high-pitch squealing sound, a "clunk-clunk" sound or what? By the way, a "klunk-klunk" sound is frequently caused by small debris stuck to the wheels of the turntable support tray. Try cleaning those wheels and the track they roll in.

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magnetron going bad, or fan blade

Make sure you tighten all the attachment screws that may have loosened during long term usage. Make sure the fan is running properly and not causing undue vibrations. Use WD 40 on the fan.

Remove cabinet cover and observe what's going on.

very possible your magnatron is faulty. Disconnect 2 transformer wires and make sure they dont short. try the program again. if no noise, replace magnatron:capacitor and HV diode Please i strongly suggest an electrician help you as it is truely dangerous in there. .

Chances are the blades are loose on the shaft or the bearings may be getting dry.

Safety & disassembly:
http://www.microwavedisplay.com/safety.txt
http://www.microwavedisplay.com/disassembly.txt

You can usually find helpful exploded view diagrams and order parts by entering your full model number here.

There should also be a "mini-manual" (tech sheet) hidden inside the unit behind the control panel or hidden on the left side behind the grille, which is very helpful when troubleshooting, testing, and locating components.

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

it may be the fan/fan cover assembly or it may also be the magnatron, after a while of use, before faulting the plates inside dislodge and can rattle around while in use.

It may be the stirrer in the ceiling area.

You can find helpful exploded view diagrams and order parts by entering your full model number here: http://tinyurl.com/gv383

If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info at our site, which is linked at our listing here on FixYa: http://tinyurl.com/yzjozk