They also contain Thorium on the end of the internal electrode. It's slightly radioactive and might set off the radiation monitors at the scrapyard.
There's been differing results to this, they have set them off sometimes in some yards. Not for me, but one yard I took them to were not interesting at all in buying them. They told me "Not to bring them in again".

I didn't know about the Thorium or Beryllium at the time. I just saw the 80 grams of near solid Copper.

Very old magnetron's, military and commercial radar systems used Gold plating inside them too. I expects that there's none in cooking microwaves though.