Bubble in sidewall - aluminum ring?
If your run flats are Goodyear, I understand they use an aluminum ring in the sidewall. If it hits a pot hole, it may 'dent' the ring, leaving the appearance of a bubble (1/8 inch rise over about one inch). Happened to me, and I drove on it for a few months, with the bubble never changing. Probably safe for normal driving. But then with safety inspection coming (tires are checked --> flunk?), I replaced it. (Rim was OK.)