One of my pet hates about Visual Studio is that it assumes that you organise folders in projects according to namespaces and adds folder names to the namespace declaration for classes. Worse still there is no way to turn this behaviour off.
Usually I get by this by adding my classes to the root of the projec then dragging them to the relevant folder, and I strongly suggest that developers working for me do the same. This week I came across a developer who complained about this and come up with reasons based around the lack of tool help if they forget to do this, so I decided to write an addin that automagically sets the namespace declaration of new C# classes added to match the Default Namespace setting in Project Properties. I have called it Clean Namespace and published it on Visual Studio Gallery
No commands, menus or UI it just detects when a new C# class file is added to your project and changes the namespace declaration. You can turn it off simply by disabling the addin via Tools, Add-in Manager...
Download Clean Namespace Visual Studio Installer