i had clicking sounds issues on my MBP. (MC374, 13", 2010-Mid) now solved the problems. want share my experiences. 0. installed Intel X25M G2 (SSD) - 9.5mm - Main HDD Bay 1. WD Scorpio Blue (WD5000BEVT) - 9.5mm - 2nd Optibay 2. WD Scorpio Black (WD7500BPKT) - 9.5mm - 2nd Optibay SMS(Sudden Motion Sensors) disabled. 1. when i finished install WD5000BEVT to Optibay. disk drive clicking every 8 seconds. -> i tryed install hdapm and it stopped clicking and i need to upgraded WD5000BEVT (Blue, 5400 rpm) to WD7500BKPT (Black, 7200 rpm) 2. after i changed WD7500BPKT. disk drive are clicking again every 1 minute 30 seconds. i tryed to hdapm again. SMS disable/enable and blah blah. it doesnt works. -> installed WD7500BPKT on my PC and disable IDLE3 modes (with WD IDLE3). and reinstall to MBP. okay it works fine. never clickings again. WD says don't apply except WD Caviar Green (3.5"), but it works same issues in Synology NAS (based Caviar Green). it designed same technologys (WD 3.5 Green, WD 2.5 Blue , Black) WD7500BPKT WD5000BEVT thanks.