Diagnosing a Slowly Failing Drive

[enter8]

WD4003FZEX (black, 4 TB), crunching (not clicking) noise, small transfers (up to 100mb) will transfer, but they'll take up to 20 minutes. As I keep working with the drive, it will stop responding completely and disappear from disk manager.

While still readable, I was able to do a directory tree of the entire drive. Also, in the preceding weeks where the drive has been slow, but, less noticeably slow, I've been running weekly smart checks. No errors whatsoever.

I have a pretty good idea of what it might be, but I wanted the forum's thoughts first.

[Lardman]

Assuming there's nothing wrong with the power delivery, weak heads or physical damage to the platters. Rather than no error whatsoever what are the smart actual values from something like crystaldiskinfo.