I didn't see a final 'What was it?' with this post, so I thought I would share my experience.
I came across this blog, because I was essentially suffering from the same conditions as creativour, only difference was that my SuperFlo is a 1.5 HP model.
Thanks to this blog, I don't think I have sufferred as bad.
After the first day of running with no issues, the second day, it would not turn over.
My Superflo made similar sounds.......the hum, with no movement.
I then found this blog...and performed the following.
I removed the filter basket and I found sand in the bottom of the filter basket area.
Removed the cap off the rear and rotated the shaft, it was the sand !!
I could feel it in the rotation....as soon as I moved it, I felt the grit, and then it became free.
Pump is running fine now!!
I should also note, the prior owner of this property put in the in-ground pool, and I have to believe he did it himself.
When I purchased the property the pool was covered, and I never really paid attention to the 'pavers' he had as the frame to the pool itself.
These concrete pavers are held in place by sand, (roughly a 1/16 of an inch between each paver), and thus, this pool is constantly getting sand in it :grrrr:
Thanks very much for all the insightful comments in this blog, it definitely avoided me many more hours of frustration and contacting the pump manufacturer!!
Murph