Oh, I have a Panasonic NN-GD38 that only beeps once. Sometimes I forget my food in the microwave because of it though. It's the best microwave I've ever had (also the first time I've ever spent so much on one).
Not OP, but most LG microwaves allow to turn sounds off with a special button combination. Even though my model's manual doesn't mention it, I could guess it from other manuals and YT videos.
I leave it enabled though because it is not continuous and has like a TADA.WAV kind of vibe. So happy!