Unity3D 3.5 Sound / Physics BUG

[http://youtu.be/-SEBxSCGNKQ][1] [1]: http://youtu.be/-SEBxSCGNKQ

as seen in that video, Unity 3D sometimes refuses to play the sound. Sometimes the sound are too low. I set the audio listener and audio source (music) at the camera. My Sound Properties : No 3D Sound, Compressed in Memory, OGG. Usually, this happened when my computer memory is full (2.9GB used of 3GB Memory) or when 100% processor usage.

Collider Problem
When the ball is getting fast, it will bounce for some unknown Reason. Mesh Collider (No Convex, no smooth, No Material Selected)

the ball also sometimes can pass (didn't collide with the track collider) the track without reason (When the ball getting fast, usually at 60^ ly). This can happened at any time.

Please help me...