Take 2 or 3 thread
dumps of Eclipse. Compare the resulting dumps. What you are looking for is whether the same thread is always active. Which thread it is and what that thread is doing might give some clue as to the problem.
My guesses as to the problem are:
a) Your eclipse is corrupted. Fix: download and install again
b) You have a bad system DLL. Most likely a driver, most likely for the network card (though usually I see hangs, not high CPU usage, with this kind of problem). Fix: install the latest drivers
c) You have a corrupted DLL. This could be caused by a virus. Fix: depends on the virus.
In general, this problem is not typical. I have run Eclipse on mltiple PCs, none of which showed this problem.