I would highly recommend clay barring it before any rubbing or polishing compound. That back ledge on the hatchbacks are a magnet for paint contamination. I usually claybar just that part of my car once every couple/few months, whereas I only claybar the whole car maybe once a year. Any detailing clay will remove those dots/bumps you are talking about.
PS--make sure you wash the area first, clay bar it, then wash, then wax. Clay removes any wax you have on the car in addition to contaminants, so make sure you re-wax.