The popping sound was probably the high voltage rectifier diode failing.
If it's bad, the symptoms you usually experience id that it runs but won't heat. It may hum a little louder, or even a little less.
If you or someone you know wants to look into this, we have *critical* safety, disassembly, and troubleshooting info at our site, and our link is at our listing here on FixYa:
http://tinyurl.com/yzjozkYou can usually find helpful exploded view diagrams and order parts by entering your full model number here:
http://tinyurl.com/gv383There should also be a "mini-manual" hidden inside the unit behind the control panel, which is very helpful when troubleshooting.
A typical diode is shown below.
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