Yikes Gene! I hope it goes smoothly without too much uncomfortability or nervousness. My experiences are also that the only background checks I've heard of were by phone.
I'll share one story told to me by some former high school classmates. My friend was taking a job with the CIA (after Dr in astrophysics at Berkeley). He listed mutual friend as a reference. Job applicant told friend to "tell them everything and anything, because they will find out
anyways".
So they called him at work. They go on and on. Friend finally had to stop the conversation with, "Can I please call you back when I get home? Id
really love to talk about this, but I'm at work!!!".
I've met a co-worker of said friend, and she said that everytime she needs to pee, she must shut down computer, remove hard drive, store it in the locker. After pee break, unlocks locker, re-installs drive, boots computer.
I have another friend who works for a private company that is contracted with the government. Not even his wife knows his job title... crazy world..