The theme maker used Cityscape sound effects you will need to scroll through the different sounds and use the test button to figure out which sounded is you do not like and change it. This tutorial should help you out Sounds - Change
Here are a few screenshots to.
For the background look at Post #6 of this thread Windows Explorer Properties window background color
I just showed someone else how to change that background.
Basically follow what I have their accept your image number will be #902
and is 50px x 50px image.
You will find .msstyles here
C:\Windows\Resources\Themes\Dark Soft\Dark Soft.msstyles
The Dark Soft Folder and .msstyles will be which ever one you used (big icons, little icons, squared big, squared little)
If you need more help let me know