CPU 100% but when i open profiler it down to 20%

Unity Engine
1

i make a u3d exe. run sometime,cpu become 100%. so i make a development build and check on autoconnected profiler. run the exe and when the cup become 100%, i open u3d profiler, soon cpu become 20%, and i can not found the reason. if i run the exe and open profiler, cpu never become high.
i will creasy. i use u3d 5.0.3 32bit. i use AVProWindowsMedia to play movie in my exe.

2

who knows