The problem doesn't occurr all the time for me. It seems to happen only when I leave my machine running a guest OS and the host goes to sleep. At that point the vmnet-natd goes 100% and after a few minutes the fans kick in. The machine is not fully asleep - just the display turned off with this task preventing full sleep.
Waking the machine with mouse or keyboard and then shutting down Fusion completely (all guests and then Fusion itself) stops the task and everything returns to normal. I can then restart Fusion and proceed as normal.
