Sound on my Laptop

[knip]

Ive got a 18month old laptop, and it has this weird habit of turning the volume off at random intervals, not muting it, just reducing the volume down so I cant hear anything, I certainly dont alter anything, it just seems to do it like half a dozen times a week and for no apparent reason. Then I have to click on the toolbar at the bottom to turn it back up.
Any idea why?

 

[knip]

Yup sounds different, the volume on the toolbar at the bottom, the level of it gets physically turned right down, without me even touching it.

This is what im talking about

The bar that adjusts the volume actually gets physically lowered but im not the one who does it. I live on my own and there is no one else who has access to this PC.