I do have a scan tool set up on my laptop that allows me to watch the A/C clutch commanded state. The noise occurs between 70 and 85% throttle. I configured the scan tool to read out throttle angle, engine torque, A/C clutch state, and engine speed. The suggestion about the A/C clutch partially disengaging was excellent and that's exactly why I hooked up my scan software last week. I figured the noise was occuring at high rpms at WOT when the computer commanded A/C off. Unfortunately its not, the A/C should be fully engaged when I'm hearing the noise. Unless the clutch mechanism is fail safe so that it must be "held on" which could mean it is partially slipping under those conditions. Once you hear the loud noise condition you can actually hear some grinding noise all the time under all driving conditions with the A/C on. More than the usual compressor noise, in my opinion. I really think the compressor is junk, even though I know it is a brand new delco part installed by the dealer. Perhaps their quality is headed down hill, in my experience AC Delco OEM parts are usually quite good.