I have researched this relentlessly and my specific scenario seems to not be anywhere.... I own an early 2015 MacBook bro (16gb RAM, 3.1 i7) Just yesterday it stopped detecting my 2TB seagate hard drive. The day before that it was working fine. In fact the last time I used it I had copied 40gig worth of files over to it. Worked completely fine and I ejected it. The next day when I plugged it in my Mac would not mount it or recognize it in Disk Utility. Here is the kicker... It shows up in my USB Device Tree. If I launch disk utility while it is plugged in then it loads forever. If I launch Disk utility before I plug it in, then it simply won't show up. It is important to note I got it to work once. Not sure how, I simply restarted the computer and plugged it in again and it worked. However, next time I tried it did not work and still hasn't up until now. I'm on the road and unfortunately only have access to this Mac. UPDATE: hilariously enough. After copying all the files to my new hard drive the whirring has completely stopped when I use my old hard drive by itself. Before transfer it took my computer a good 10 minutes just to load the files on my hard drive. Now that is completely gone too and it seems to be working perfect now. I still won't use it to be safe... but it's kind of frustrating to say the least.