Silent Stones?

I asked this last night in the Building Tips forum and got zero responses, so I'll give it a shot here.

I was playing around with dropping physical spheres onto nonphysical blocks in each of the different materials. Some of the built in sounds are interesting, but I noticed that the stone-on-stone collision didn't make any sound. Is there supposed to be a sound there, or is this a known issue that it's missing?

I can hear the sound 9538f37c-456e-4047-81be-6435045608d4

I think these sounds are throttled to prevent spamming.

Torley mentioned something about this in one of hir vidtuts recently. This one, probably, http://www.youtube.com/watch?v=kSg9ENSeBCY .

In the Edit window, on the Object page, there's a place to select the material. It defaults to wood. All of the materials make a sound when there's a collision except the stone, so it's not a result of the throttling.

OK, after a couple extra restarts, I'm getting sound from the stone material now. It's odd that stone was the only one of the 7 that didn't give me any collision sound before.