I've aways pronounced it as "sub-ett-ah", I have never once considered it might start with a "soo" sound.
[flower=AceOfSpadefish] [ToT=AceOfSpadefish]
I've always said it soo-bet-uh. I joined when I was like 12 so idk if that's how I would say it if I saw it for the first time now 🤔
Soo-Bet-Ah person here :)