Still ongoing.... I have tried every combination in all of these suggestions, including my own. Still not fixed, but two observations:
1. Since updating to Mavericks, my internal iMac HD has been running nearly non-stop, no matter what I've been doing or not doing. I presume that it's (still?) indexing? All external drives have been excluded, also half th list that Apple provides for the internal drive. But neither Spotlight nor anything else shows up in Activity Monitor as being the cause. Don't know if that's related to TM, but it might be.
2. I checked with WD by telephone. They insisted that I remove WD Disk Manager, so I did -- no difference. In rummaging around the WD site, I noticed that some of the newest WD drives have firmware available that clearly states that it fixes the Mavericks problem. If you use WD drives, check out http://support.wdc.com, search for your drive; if yours has a firmware update, and it works, let us know. My drive, being 17 months old (you know, back in the Dark Ages), does not have a firmware update. WD insists that they will have one.
To my observations and analysis, this is clearly an Apple Mavericks problem. Drive firmware may contribute, but the only single consistent conclusion is that Mavericks has a serious bug in it. I'm looking for Apple updates to Mavericks, but have seen none yet. I don't know if they are working on this problem or not.
For what it's worth.