I've got hub caps but I don't think it would be a rock inside as they have breathing slots in them. As I begin to drive off the tick is very consistant.
The sound reminds me of when I was little and was riding my bicycle with a playing card clipped on the post and when you start to move the card would tick. The faster you went the more the ticks.
As far as drag, I can be going down the road and let go of the wheel and it stays rather straight.
Would warped brakes make a tick sound? It's definately annoying tick that gets less frequent when you slow and speeds up when you do.
