I just wanted to say that I have THE EXACT same problem!
It's usually during a time where my adreneline peaks quickly, like a confrontation with someone in anger or an almost car wreck, etc. The first few times it happened I thought I was going to pass out from the
pain. It's localized around my kidneys and it's sudden onset, lasting for a few minutes after the intial stressor occurs.
I have brought it up to my endocrinologist and she said she has no idea what it could be, but if it continues she would order a CAT scan of the adrenals. I wish I could envoke the sort of stress that triggers it while hooked up to some test! LOL.