Pi 3 - Hardware Error when Connecting Two Identical WD Passport USB Drives

[uareingdale]

A hardware (driver) issue when connecting two identical WD Passport USB 4TB drives to my Pi 3.

Have a Pi 3 and two (new) identical WD Passport USB 4TB Drives.
When one of the drives is plugged in, works as expected.
When the two drives are plugged in (Doesn't matter which is plugged in first, or which USB port); then, the second drive starts a clicking sound and does not work intermittently. It may be detected, formatted, and seeing by GParted. But GParted may show errors when scanning or FDISK may not see the drive.
I returned the drive that was making the clicking sound; got an identical (new) drive, and ended up with the same issue.
Tried the drive (making the clicking sound) on a Mac and was able to use as normal (formatted and transfer gigabytes of data back and forth over a weekend)
Re-downloaded the Pi image, redid the Pi and did all over again to end up with the same clicking sound.

[neilgl]

Are those drives using a separate power supply?

[klricks]

What is the power or Amps rating of the drive?
The combined total current capacity of the RPi USB ports is 1.2A which usually limits the number of USB drives to 1.