Compressor whines over 2k

Hi. When I'm driving and the a/c compressor kicks in, if the rpm is over 2k then it whines, louder and higher for the faster the engine is running. I usually turn it off when I take off, because I'm afraid I will damage it or something, and turn it back on when I'm done accellerating. But when I'm on the highway going 65+ it whines all the time, because there isn't another gear. Does anyone know what this is? I got the compressor rebuilt from Auto Zone last year.