I'm having a whole host of problems with an external hard drive that was working just fine a couple of hours ago. I've had this problem before once, and that was about 3 months ago, here's what I documented:

So a couple of hours ago I turned off all my computers and shut off the power to all my devices in my room, then went and turned the power off at the main switch so I could change an outlet.

A couple hours later, after I've already slowly turned everything back on, I go to my xbox to try and watch a movie and it can't seem to list any of the movies I've got. So I go to my desktop to find that my external hard drive isn't there.. even though it's on and connected. It's also stationary and hidden behind something so there's not a whole lot of tampering/physical wear to that external.

I plug it into my laptop to try and see what's going on. It starts making this endless loud screeching noise. None of that clicking that's usually associated with hd damage. It's not listed in my computers, and it shows up in Disk Management as "uninitialized" asking me to choose between two different partition types. After carefully disconnecting it and connecting it back, it asks me to format it, which I cancel.

I start googling about my issue, starting to accept the situation, torn as hell and helpless and just about ready to toss the thing.

Suddenly the screeching stops, after almost 45 minutes of it going, and Disk Management lists the drive as "Online" and "Healthy". Explorer pops up with all my files! I'm still being really careful with it and weary and treating it as though it's in fragile shape.

I've downloaded some S.M.A.R.T. software to read the values and everything is listed as "OK" . No reallocated sectors, no read errors, no seek errors. I also ran a quick self-test, which completed without error. Everything seems fine.

It looks to be a perfectly healthy external hard drive.

So what the hell was that about? Was it doing some sort of maintenance or self-test? How am I supposed to tell the difference? I would've undoubtedly killed the drive for sure if had it gone on a bit longer.

I've got the same problem now, with one exception: it doesn't magically reappear after the screeching stops. Occasionally I manage to get some S.M.A.R.T. diagnostics information, which basically reads everything as fine. The only problem is that my HD isn't initializing (so I can't access anything in it). I'm able to successfully run a quick smart test but not an extended one (I've only tried it once but got conflicting indications as to whether it was actually making any progress or not (was stuck on Random read test).

So, final question (if all else fails): Could the hard drive enclosure be failing rather than the HDD? Is this a likely possibility at all? How would I know?