The ground that doesn't have stepping sounds in 0.45 experimental:
http://i.imgur.com/55fVrHS.jpg
And the surface, which had broken sounds while it was raining was a black, concrete road, which goes trough the new town released in 0.45 and some other towns.
You have to run in the middle of the road the audio glitch to happen. I don't have a picture of the road right now.