Errors in sound with avi's made by Powershot a60

[basics]

I won a Powershot a60.
With every movie I made , there are light errors in sound to hear, a rumble.
It is difficult to explain, so here a demo to download:
http://www.djeduardo.nl/test.htm
Is this normal? ANd if it's not, what to do?

[PeterS45]

Nothing strange to hear. There's no sound to be recorded and therefore the camera tries to pick up any sound he can. It's like opening the volume on your radio when the signal is too weak. When there's enough sound to be recorded, like somebody talking, the camera will have something to set the volume on and then the sound will be better.

[basics]

This is not true..
because I have made very, very much movies, in very different situations, and the sound is everytime exactly the same.
It is a rumble, or something...
But I heard more users knows this problem.