These files are generated by NCrunch when it loads your project. Basically, NCrunch doesn't tamper with your existing project file, but it does need to make modifications and save these to disk before it can invoke MSBuild.

So we have a temporary file that can exist for a few seconds, depending on the time it takes to load the project.

If for any reason NCrunch doesn't clean these up (i.e. if it gets terminated or something goes horribly wrong), you can safely delete the files.