Oven appears to be in constant standby mode. Clear/Stop does not fix it.

Here is a section of the manual for your microwave on child lock, hope this helps.
"L" - Page 7 Press and hold STOP/CLEAR until " L " appears on the display and a BEEP sound is heard. The CHILD LOCK is now set. The time will disappear on the display . To cancel CHILD LOCK press and hold STOP/CLEAR until " L " disappears. You will hear a BEEP when it's released. If any button is pressed, "L" will appear on the display Your oven has a safety feature that prevents accidental running of the oven. Once the child lock is set, you will be unable to use any functions and no cooking can take place. However your child can still open the oven door. Press STOP/CLEAR. Child Lock 7

" 1. CHILD LOCK
The Child Lock prevents unwanted oven operation
such as by small children. The oven can be set so
that the control panel is deactivated or locked. To
set, touch Custom Help, the number 1 and Start/
Touch On. Should a pad be touched, LOCK .
.. ON will appear in the display.
To cancel, touch Custom Help and Stop/Clear. "

Also, to find manuals........

Unplug the unit or shut all power off to unit and then restore power as this should solve your problem.

As with most situations, it depends on the model number, but try this:

To set child lock:

1. Touch STOP/CLEAR pad.

2. Touch and hold 0 pad more than 4 seconds. LOCKED will appear in the display window and oven will beep twice.

To cancel child lock:

1. Touch and hold 0 pad for more than 4 seconds. LOCKED will disappear from the display and the oven will beep twice.

Demonstration Mode
This is to enable you to experiment setting various
programs. (The letter D will always appear in the display
window. This is to confirm that there is no microwave
power produced and it is safe to use the oven without
any food). To set Demonstration Mode: press micro
power once, then press Stop/Cancel 4 times. To cancel
Demonstration Mode press Micro power once, then
press Stop/Cancel 4 times.

The Child Lock prevents unwanted oven operation such as by small children. The oven can be set so that the control panel is deactivated or locked. To set, touch CLOCK, the number 1 pad and then touch the START pad and hold for 3 seconds. Should a pad be touched, will appear in the display. To cancel, touch CLOCK, the number 1 and STOP/CLEAR pads

There are loose laminations in the transformer causing the noise. A replacement transformer will stop the noise or indeed re-crimping the cover on the transformer will possibly clear the noise.

Hello :

Many models of the GE microwave have sensors that can detect humidity from the foods you are cooking. This allows the microwave to make adjustments to the power levels used to cook your food. If "Sensor Error" appears, you should either press "Clear" to cancel the mode or leave the food in the appliance longer to give the microwave more time to detect the food.

Press "Time Cook" to manually enter the time if you receive an error message when trying to use the "Sensor Reheat" mode of your GE microwave. The error message may be caused by the food item being too large or too small to detect..

good luck .

please rate !

The control lock shuts down the control panel pads to avoid unintended use of the microwave oven. To unlock/lock control, the microwave must be in standby mode, touch and hold stop/clear for 3 seconds until one long tone sounds and the display clears to show an outline if the display area. Repeat to unlock control, and return display to the time of day, if any pad is touched while the control is locked, there will be no response from the microwave oven. hope this helps.

The manual says "while in standby mode, press and hold the '3' key on the keypad for 3 seconds until 2 tones sound and the 'DEMO' icon appears. Repeat to turn demo mode off."

You can download a copy of the manual here:

http://shared.whirlpoolcorp.com/assets/pdfs/literature/Use%20and%20Care%20Guide%20-%208206572.pdf