Do you know for sure that your AC system is fully charged? It'll cut out at higher rpms if you're low on freon, most likely cause of what you're describing here.
The noise? It might not even be directly related to your AC system. Sometimes when the AC compressor's running, other things can resonate noise and it might be something as simple as a shield vibrating (guessing). Without hearing it, it'd be hard to guess that right from here.