I recently serviced my rear wheel.
Applied new grease on the hub.
After I was done I noticed when I spin the wheel it sounds like sand is falling through the wheel.
I removed the rim strip, cleaned it and still hear that noise.
I find it hard to belive that its the hub since I just cleaned it.

Could it be the tension of the spokes?
Damage to the rim itself?

I don't know how long its been doing this I didn't notice it until I service the hub.
I serviced the front too but there's no noise there.

Anybody have any guesses on what could be causing this.