My late 2012 iMac has been running great for the past 4+ years, until last week, when it suddenly started running slowly, hiccuping at the simplest of tasks (opening Safari, loading an image in Preview, creating a calendar event, etc.). Then the computer started making a clicking/chirping noise. I verified and repaired the HDD, booted in safe mode, and the problem persisted. After poking around the internet for advice, I separated the SSD from the HDD so it's no longer a Fusion drive. I had already backed everything up, so I decided to wipe the HDD with Disk Utility and start with a clean slate. So I started to format the HDD - just a single pass of zeros, not the high end security settings. That was two days ago, and it's only about a quarter of the way through the one pass of zeros. The drive is 3TB, but I imagine it shouldn't be taking this long. Do I have any other options other than just waiting a week for it to (hopefully) finish formatting? Or is this a sign that the HDD is bad and I should just replace it? Any help is much appreciated!