Hi, I'm no stranger to upgrading my Macs (been doing it since 1989). I've followed this guide too since the inside of my '11 iMac is a little less upgrade friendly and my fans spin up afterward as well even if the computer is just sitting there idle. I replaced my factory internal 500GB WD drive with a 2TB WD drive. It doesn't take long before my fans start to spin up. I've checked and rechecked all of the cable attachments. What else could I be doing wrong? What are your referenced recommendations that take care of this with a hardware solution? My best find so far is a donation based version of the above mentioned S.M.A.R.T. tool (http://exirion.net/ssdfanctrl/).