I went out for a ride today and on the way home the bicycle started to make a terrible noise. I took it home on the stand and pedaled it. There was a loud dragging noise coming from the wheel. I turned the wheel by hand, and as it turned, for about 45 degrees of the rotation, it got tight as if it were dragging. After that 45 degrees, it rotated easily again.
There is nothing rubbing against the tire anywhere externally. I took a lot of time and verified nothing was rubbing against it but I do feel the resistance as it turns. If I pedal the bicycle fast, the rear wheel has enough wobble to make it shake the stand.
There is a lot of grease coming out of the hub. I had it at the LBS for a tune two weeks ago, I do not know if they added extra grease.
The bike has a shimano single speed coaster brake hub.