(This is unfortunate because Panasonic seems to be the only brand that can actually adjust power output, whereas the others simulate lower power levels by cycling on and off.)
Inverters themselves are potential noise sources though so may be part of the issue but other implementations may not interfere.
The traditional design needs all power to go through a transformer. A 1 kilowatt 60Hz transformer necessarily uses a lot of copper and steel. The inverter design can use MOSFETs (theoretically cheap, but a reasonable IP cost) and far less copper and steel.
Mine emitted white smoke warming up some tea while I was in another room. I hope to God it wasn’t beryllium.
I still have a Panasonic OTR microwave, but it’s inverterless. It appears to be an improved design of a GE model from the same OEM.
Happens frequently when the mica sheet that covers the injection port gets moisture from steam (who'd have thought - steam in a microwave?!?)
Simple fix is to replace the mica (a few cents from AliExpress) and use steel wool to get rid of any carbon residue around the injection port.
There was indeed a char mark on the mica sheet, but the beryllium terror at the time was enough for me to chuck it.