They recently tore down the office walls to make a fully open office where I work. I went from my safe little closet of an office -- it was way too small but I had my back to walls, so I was more than okay with that -- and now we're out in the open. In the noise. In all the activity. I can barely stand it. My co-workers think I have severe intestinal problems with how often I go sprinting for the bathroom, just to find a place with a door to calm down. I do a lot of breathing and grounding exercises, and print at the far printer "to get some exercise" but really just to have an excuse to move.
My boss has the emotional intelligence of a teaspoon, so he makes it worse. On advice from HR, I'm working with my T to get the FMLA paperwork in place and hopefully they'll make some accommodations for me (the boss won't help in a non-official way, hence the paperwork). That won't be an option for you when you start a new job, as I believe you have to have worked there for twelve months.
The only thing I can suggest is practice. You might try going to the library, sign up for computer lab time, as a desensitization technique?
Edit: you don't necessarily want to ask for too many accommodations when you first start, but you might check JAN to see if they have any easy options that you might be able to do on your own to start.
