Yes, me too. Not sure about the onions, but definitely metallic, almost bitter. Sometimes I’ve put a glucose tab or cookie in my mouth and had to quickly double-check the packaging to make sure I haven’t accidentally ingested poison. @bkh recently described the same thing. I don’t have a titanium plate.
This was also my problem for years and years and years and years. Low = gorge. It was like the brain sent out just one command to all my body’s cells: EAT SWEET THINGS. Then I discovered it really only took two glucose tabs. Or maybe only even one. Not four like recommended; that was way too much. Two tabs, wait a bit, and it was all over.
Once I got my CGM, of course, I rarely got that eat-everything low in the first place. Problem solved.