What Lurks?

So I'm driving home after a late night run to my shop and I here
scriiiiiiiiiiiiiiiitch. And a few seconds later I here
scriiiiiiiiiiiiitch again. And then it starts to form a regular pattern
and I'm like Aaaaagh! It's the CLAW MAN! I'm freaking out turning my
head without trying to wreck the van to see who/what is making the
noise. Yeah, about the stop sign I realize the back window wiper is
going on a dry gravel dust covered window. No claw handed man.