The burp if i'm not mistaken is a sort of grinding sound right after you start the car. Sounds like belts grinding, but its not..It only happens during cold weather starts. And when the car has been sitting in sub freezing temps for longer then 6 hours or so. One morning about a month ago, it was 8 degrees and my car had been sitting for 12 hours or so and I started it and it made a huge burp, more like a sneeze...Right at that moment my valve cover gasket blew. I didn't find out until I pulled over on the freeway with my car smoking profusely...that was not a good day.

However, the oil seperator is known to fail in warm temps and climates too. It is not strictly related to cold weather only. It is just more likely to fail in cold weather..But I've never had the burp in warm temps...