A/C Compressor Question

I have a slight rattling sound coming from the bottom of the engine/transmission area. I notice it occasionally at idle. I do not really notice it while driving, but I am thinking it that may be because of the exhaust and other general engine noise. I did notice it while driving up the driveway, so I am pretty sure it is not just at idle. I did some searching in this forum, and one possible culprit seems to be the A/C compressor. With the A/C off and engine running, the clutch pulley appears to rotate normally and the clutch plate stays motionless. I turned the A/C on, and the clutch plate only rotates intermittently, engaging and disengaging. I would assume that the clutch plate should rotate constantly as long as the A/C is on. Is that correct? If this is correct, what further tests should I run and what do you expect needs to be replaced? Is the car safe to drive?

Thanks in advance for your help. 2000 GT with >150,000 miles.

I checked the A/C compressor in my wife's Acura, and her clutch pulley seemed to operate as mine currently is operating. Reading some more about A/C compressors and mine in particular...it appears the clutches are supposed to cycle while the A/C is on. So, it appears that the compressor is functioning properly. Need to find that rattle. The heat shield on one of my cats may be loose. I have had that issue before, but this sound seems different. Regardless, I will try to spot weld the heat shield again to see if that stops the noise.