Oster Model # OM1101NOE, As others have asked, is there a way to decrease the volume or disable the beep?

Are you sure that Model Number is correct? There are 73 Oster Microwave Manuals here, but none of that model number designation. When in doubt 'Read the Manual'.

The kilograms settings are for meats and cakes and large objects. All microwaves have a seconds and minutes setting. Most also have presets for certain things like Pizza and Popcorn.

https://www.manualslib.com/brand/oster/microwave-oven.html

This is the search query for your model

https://www.google.com/search?q=Oster+OGGW3803+manual

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probably bad touch pad, the unit thinks your standing there pushing and holding down a button on the touch pad. Will need new touch pad or main PC board. Tough pad cheaper, more common, start there.

Disconnect the beeper speaker or muffle the speaker sound with something like tape across it.

Ask Oster at: http://www.oster.com/service-and-support/service-and-support.html

If the owner's manual does not mention this as an option, the only other option would be to disable the piezo beeper.

Here's a video showing you one way:

There are a few possibilities, magnetron, high voltave diode" sometimes cracks" high voltage capacitor " shorts"

There are three things to consider, the magnetron "heats food" high voltage diode "sometimes cracks" and the high voltage capacitor "sometimes shorts" one or more can cause the symptom of no heat. I recommend a professional to assess.

Hi and welcome to FixYa, I am Kelly.
You did not mention a model number so I guessed. Here is the manual for the 2 LB machine:
http://www.oster.com/manuals/oster/005838-000-000_English.pdf (58 minute machine)

This is for the other machine:
http://www.oster.com/manuals/MANUALS/CKSTBRTW20_43_33506787.PDF

All Oster manuals are on this page:

http://www.oster.com/ProductManuals.aspx

Thanks for choosing FixYa,
Kelly

No, that is the "waveguide cover".

It provides very important protection for the magnetron.

And always keep it clean according to your manual's instructions.

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

Ask here, it seems they can get you every Oster manual as a PDF file. Maybe they have a more detailed version?