Every few minutes there is a hum likesound coming from the bottom of the unit it almost sounds like an old oven time getting ready to go off it lasts for 15 to 20seconds

if the sounds a high pitch squeal !! I had an ole tv that did that when u watched it , finally one day the dang power supply up and gave out !! so that must be what the noise was coming from all that time !!!

Sounds like the fan motor iskills on its way out. Next time it hum without shutting the power off disconnect the fan motor and see if the humming stop.
If it does then it is the motor

It sounds like you are going to need a control board. You can look for a used one online part number WB27K5210. You can also send your board in to be rebuilt. Corecentrics and Fix your board are two reputable companies.

did it come into contact with water at anytime, if yes than this is probably the reason ask an electrician to come and have a check or if it is working fine you can continue using but make sure that no liquid will spill over inside

It's cooking when it shouldn't, but the internal cooling fan is not running, so the magnetron is overheating, which can kill it.

Then when it gets hot enough, it trips the magnetron's thermostat, interrupting all power to the microwave. When it cools, it comes back on.

If and when an oven is coming on or doing anything by itself, this is very dangerous and can result in a fire.

So until it is repaired, please leave it unplugged or leave the door open when it's not in use, and of course one should never leave a microwave unattended while cooking.

The problem is almost certainly that the power relay on your control circuit board is shorted.

We regularly repair such control units for customers nationwide by mail for $39.95 postpaid with a one-year guarantee.

Feel free to contact me directly (and please remind me of your full model number from the tag on the unit) for more free information & help.

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

William E. Miller, AS-EET
[email protected]
http://www.microwavedisplay.com
Microwave Oven Control Panel Repair Nationwide

I would advise returning it as it is still under warranty at 8 months old.

Go up on roof and using a stick or similar, poke it through the air holes in side & try to turn the fan blade at rear of the air conditioner. Make sure it's off at the time. Try to get 2 or 3 complete revolutions of the fan blades, then try turning it on fan only first,and let it run on fan for a few minutes, then switch to cool. If worse comes to worse and you can't get blades to turn, remove cover on roof (watch for wasps & bees) and spin fan blades a few times by hand, step back & have someone try fan only. If that works, then try cool. Sometimes they get a dead spot from sitting, and that will get it going again, 90% of the time. Let me know how it goes.

SOUNDS LIKE THE MAGNETRON WENT BAD IT'S ABOUT A 100 AND SOME DOLLAR PART

it sounds like its hum bars. that means you got power and rf interfearence. you'll need a ground loop isolater

sounds like you may have a bad transformer