Yesterday I took delivery of a Samsung 840 PRO 128GB. I ordered it to replace my Samsung 470 which I planned to move to the optical bay using the Nimitz caddy I got from eBay over two years ago (yes, it took me a while to decide to go this route). So, I opened up my Early-2011 MacBook Pro 13" last night. As expected, removing the 470 from the main bay and replacing it with the 840 Pro was a cinch. The other half of the upgrade was a nightmare. It was a pain in the neck working with all those small screws and, after hours, I was not able to get all the screws back in, though I put the lid back on with the components relatively snug. I fear the Samsung 470 is too bulgy for the optibay. I powered everything up and installed Mavericks onto the 840 Pro which couldn't have been easier but I encountered some issues. At one point, while using Mavericks on the 840 Pro, I lost the cursor and had to turn off via the power button. Anytime I booted into the 470 from the optical bay, it would work but my computer would run crazy hot over nothing. Although, today, I booted from the 470 and it is running fine and cool. One other problem I had last night was that I couldn't adjust the volume on Mavericks, it was at a mid volume, nothing more. The volume icon was like grayed out. I rebooted into the 470 and no problem adjusting the volume. The issue is resolved today, but the sound crackles from either drive. I remember I failed to secure the wires which run alongside the optibay and I fear that has something to do with the sound not being right. I thoroughly wish I just got a 256GB 840 Pro and left the optical drive in.