I was given a 3 year old Corsair power supply (XMPSU-650TX-C). I wanted to make sure it's working right before plugging it to a motherboard. So I did the paper clip power on trick and all the voltages were ok. I proceeded to connect just one harddrive. The harddrive spins up and then makes a revving noise every second as if its powering down and back up repeatedly. Also, theres a green LED light on the harddrive that blinks(normally its a solid on). This doesn't happen every time I cycle the power supply however. When the harddrive powers up properly the LED light is constantly on and rpm is constant. I tried two other harddrive with the same outcome. The problem is definitely intermittent. I connected all three harddrives with the same results. I tried the same setup with two other power supplies with no issues at all. I am now sure the issue is specific with the Corsair power supply. Is it because there's not enough load on all rails making the power supply unstable? The AC current draw was only 240 mA so it wasn't the overcurrent protection kicking in. The 12V line was steady but the 5V line fluctuated a few hundredths of a volt in unison with the harddrive revving. The 5V line was steady when the harddrive powers up normally. I'm hesitant to connect a full computer to this. Anyone have an idea before I try to RMA the power supply? Is this just a peculiarity of this model?