The fan should spin pretty freely but I don't think it goes for a long time after you stop applying spinning force. I don't think you can spin the motor shaft without cage fast enough to get it to spin after you lift your fingers.
Did you check for axial play in the bearings? My SDL fan makes noise at anything but max. It usually stops if it gets to min. I tried the SE fan in the SDL and it works as it should. The only difference I can tell is that the SDL motor has more axial play. I didn't try the SDL blower in the SE.
As for the voltage, what does the fan see? It's a strange (to me) set-up where one wire sees constant +12V and the other wire sees anything from close to 0V (max) to something close to +12V (low). FWIW, I think I saw a max of +7.4V on max at the firewall when I was trying to figure out what was wrong with the SDL.