Background Check From Hell

I accepted a position last week and when I gave my notice on Monday was promptly shown the door.  However, my background check that I assumed was complete last week is still ongoing.  In one of my interviews, I mentioned a former client project that was relevant and heard that someone is calling them to ask about my role there (the project was public).  While I have nothing to hide, I am getting concerned calls from former coworkers asking why someone is calling and trying to get dirt on me (one thought I was going through a divorce).  I am surprised by the depth that they are going by calling not just HR to verify employment but former coworkers and clients as well.  Has anyone gone through something similar?