I finally got some decent audio recordings tonight.
I recorded a WD60EFRX unit and then a WD30EFRX to compare. In each case, I powered up the drive by itself outside of the cage with no OS or other drives connected, then hit the power button to spin the drive down. I've posted the two MP3 files on SoundCloud.
WD60EFRX recording - https://soundcloud.com/lunadesign16/wd60efrx
WD30EFRX recording - https://soundcloud.com/lunadesign16/wd30efrx
In the WD60EFRX recording, you can hear the drive spin up at the 7 sec mark and the spin down squeal starting at 32 sec.
In the WD30EFRX recording, you can hear the drive spin up at the 5 sec mark and the quiet spin down starting at 26 sec.