The pop usually indiactes a blown high voltage rectifier diode.
The humming could be normal, but if it's louder than usual it may mean the high voltage transformer or the magnetron has failed.
If you or a friend decide to work on it, we have *critical* safety, disassembly, and troubleshooting info at our site:
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You can find helpful exploded view diagrams and order parts by entering your model number here:
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