Visual Studio Unit Test: Huge startup delay in debug Mode

I'm working on a big code project. When I try to run a unit test in debug mode using nunit on Visual Studio 2013 Ultimate, there's a consistent 40 second delay before the test runs. Now, once the test starts running, it runs as fast as I'd expect. And if I run the test in Release mode, there's no delay.

I know it's a local environment problem because other developers report no similar delay when they fire up a test on the project.

I've been unable to determine what's causing this delay. The only visual evidence is that the cursor changes to a spinning cursor. I've disabled everything in Options that looked like it might be demanding. I have NCrunch and Resharper installed, but both are disabled, so neither appears to be at fault.

Any suggestions?