Yeah, I learned that real quick. I do keep moving, but it's as if someone is always magically appearing behind me. This actually happens a lot if I do keep moving. Often times it will spawn the guy I just killed right behind me. That's why I advocate staying in a certain area of the map covering the points of entry to you. Also, know where your teammates are and the spawn points to be able to figure out the most likely place the enemy will spawn.